I’ve listed some guidelines to dominant chords that beginners and musicians coming from other types of music often need to have explained to them, from the mild to the spicy.  They are not ‘rules’ but ‘guidelines’ that will help open up an understanding of what jazz players have been doing with dominants for well over half a century.

For the sake of argument, we'll talk about the key of D (two sharps), in which A7 is the V chord.

1. The essential tones of a dominant are the Major 3 and flat 7 -- C# and G for an A7. Those are the only tones an accompanist really 'needs' to play to express the V chord. Also, these are the strongest notes to target in a dominant phrase to explicitly state the V chord in the harmony.
2. A 'functioning' dominant is one that is going to its I or i chord. A non-functioning dominant would be like the Bb7 in a Bb blues, because is not the V of any chord (until it goes to the IV chord).  Another example is a II7 that eventually changes to a ii-7 before moving to the V and back to the I.
3. The dominant in a ii-V is a functioning dominant. In fast tune, you are likely to just think of the V chord instead of the ii and then the V for the cadence, especially since the ii and V are diatonic. If you target the b7 and the root of the V early in your ii-V line, you have already expressed the 'ii' via 'essential tones' (essential tones are 3rds and 7ths).
4. Any functioning Dom.7 chord can be altered with almost any type of 'extension.' The only taboo note is the Major 7 -- you wouldn't want to play an Ab in an A7 unless it was a chromatic movement (see 'bebop' scale). Traditionally, the 11 is somewhat 'weak' also. Adding a b9, 9, #9, b5, #5, 13 are all cool to add in your A7, however if you have one player thinking A9 and one player thinking A7b9, you might get some bad 'rub' if they aren't listening to each other.  The ‘outside’ notes can help ‘lead’ the listener chromatically back to the I, which where a functioning dominant goes.
5. While A Mixolydian is the 'diatonic' way to play over our A7, you can also play a BbminMaj7 scale, or a DminMaj7 scale. These are referred to as the 'altered' scale, they are just different modes of the Harmonic or Melodic Minor when you start on the A. They bring out various altered tones as listed in guideline #4.
6. You can also play a Bbdim arpeggio/chord or any inversion of it (Gdim, C#/Dbdim, Edim). This is like an A7b9 substitution.
7. You can substitute the tritone Dominant of a functioning V instead of the V7. Instead of A7, you can substitute Eb7. A tritone sub voicing is also a V7#11 voicing.
8. You can substitute the dominant rooted at any note of the V's tritone diminished arpeggio on a functioning V chord. The tritone sub in D is Eb7 (Eb is the tritone of the V, which is A). The Ebdim arpeggio is Eb, A, C, Gb. For the A7 five chord, you can sub Eb7, C7, Gb7. As stated in guideline #7, Eb is a A7#11 voicing. The C7 is A7(b9,#9). The Gb7 is A7(b9,13).
9. Because of #6 and #8, you can play the A Half-Whole diminished scale for a A7 (A, A#, C, C#, D#, E, F#, G). If it is easier, you can think of this scale as E Whole-Half scale (E being the ii chord).
10. Pretty much any diatonic chord can be re-harmonized as a dominant. The vi chord can be played as a VI7 (A Train). The ii chord can be played as a II7 (There is No Greater Love). The iii chord can be played as III7 (All of Me). I can't think of a vii chord going dominant, but the bVII7 dominant is the 'back-door' dominant that can resolve to the I (G-7 / C7 / Dmaj7). Remember C7 is one of the 4 dominants out of the tritone diminished in guideline #8.
11. You can play the whole tone scale on Dom7#11 or Dom7#5 chords (A whole-tone on A7). It can sound pretty 'out' if the rest of the band isn't hip and seems to work better in some scenarios.
12. The melodic minor has 2 diatonic dominants. The MM IV is Dom7#11, the MM V is Dom7(b13). For playing Bb melodic minor over A7, you can try Eb7#11 or F7b13. If you were thinking E Harmonic minor, you could try A7#11 or B7b13.
13. The Barry Harris 'Six to Diminished' concept re-harmonizes the diatonic chords to either be a 'Sixth' chord or Dom7b9. The 'V' chords are played using ‘diminished’ voicings with the V's b9 as in guideline #6.  The diminished voicing of the V always leads to the neighboring inversion of the I6 voicing.  There is an extra chord inserted to account for the #5 of the 'Barry Harris' scale explained later. For D major, the chords are all the B-6 inversions (which serve as the I, III, V, VI chords), plus all the C#dim inversions (which serve as the II, IV, bVI and VII chords). So in D Major: I = D6, II = Edim (A7b9), III = F#-6 or F#maj6 (don't voice 3rd – and inverted I6), IV = Gdim (A7b9), V= A9/11/13 (inverted I6), bVI = A#dim or Bbdim (A7b9), VI = B-7 (inverted I6), VII = C#dim (A7b9). This creates a chord scale that is constantly descending from V (A7b9) to I (inversion of D6). It diatonically relates to the 3rd mode of the Harmonic Minor Scale (minus the 5). So, the 'Barry Harris' Maj#5 scale is the VI as Harmonic Minor. For D, the Maj#5 Barry Harris scale is essentially B Harmonic Minor (plus the A note). This scale has all the B-6 and C#dim inversions listed above.
    

Nice blog article on visualizing the fretboard for jazz:
An Origin of Patterns

The attached PDF shows some simple, useful chord moves for ii-V and iii-vi-ii-V progressions.  Here are a few reasons they are so useful:

1) They feature a strategy where you are only moving 1 finger on a grip.
2) They feature voice-leading -- the finger you move outlines a chromatic descent to the next chord
3) They expose how a small vocabulary of chord shapes can be re-used for different voicings

As I've mentioned before, the first teacher who attempted to teach me about jazz guitar recommended the Mickey Baker books.  While they were nice at getting some basic and hip sounds going, there were a lot of holes to be filled.  While I don't particularly recommend starting with them, the best thing about his books was he gives a relatively small number of chord shapes to learn and re-uses them to stand-in for different chords in a hip way.  The first page of the PDF attempts to show how his chord shapes can be used in a ii-V progression.

The 1-finger ii-V is at the heart of what he initially presents, using a min6 as a Dom.9 voicing.  Making a min7 chord (acting as the ii) into a min6 chord (by moving the chord's b7 down 1 fret) gives you a rootless Dominant 9 chord, which is used as the grip for the V chord in the sequence.  Mr. Baker also shows that if you just hold or reposition min7 chord, you end up with a  rootless Dom11 chord.

As you may know, the min6 chord not only sounds like a Dom.9 chord, it is also a half-diminished (min7b5) voicing. The second page of the PDF shows all the various ways the min6 and min7 chords can be interpreted.  Understanding other uses for any grip you learn is a great thing to do.

Page 3 gives a few variations on a iii-VI-ii-V progression with Mickey's chord voicings.  This is the next most essential progression to learn after the ii-V.  Once you learn and hear the 2-5 and the 3-6-2-5, you will be able to abstract away several measures of many jazz standards which will make them easier to learn and remember.  Instead of learning several measures of a standard, you can eventually just represent it in your mind and ear as a 3-6-2-5 leading to a tonic.  If the six chord is a Dominant (has a major 3rd), then the 3-6 is like a ii-V going to the 2 of the ii-V which then goes to the tonic.  

Mickey's variations include using a min7 shape moved down one fret to represent the tritone of the ensuing V chord.  This tritone works out to be a Dom.7(#9) voicing.  A more common written variation is to use a rootless Dominant #11  for a V, which also happens to be a Dom.7(#11) a tritone away.  In addition to using a half-diminished (min7b5) shape as a rootless Dom.9 chord, we also see how a min7b5 shape can be grabbed as  Dominant Altered chords.  Finally, we see that the iii-7 chord can be a Maj9 voicing for the tonic.

Ideally you want to work out similar chord moves for every inversion of these chords.  The remainder of the PDF will give you a start in that direction.

Page 4 begins the chord moves for a I-vi-ii-V in one position for all the basic inversions which are in the Jimmy Bruno Inversions dictionary (you should check that PDF out if you haven't already).  This should allow you to do this chord move anywhere on the neck for any key.  Remember that the vi-7 chord is homonymous with the Tonic as a Maj6.  The squiggly arrow shows you will have to move up some frets to get the chord root on the correct note.  The min6 of the ii is equivalent to the Dom.9 of the V chord (as well as the other homonyms shown on Page 2).

Page 9 shows a 3-6-2-5 progression with altered dominants as the 6 and the 5.  The squiggly arrow is to alert that you will need to move the shape down on the neck to get the root in the right place.  When the 6 and 5 of a 3-6-2-5 are dominants, the 'tonal center' is located a whole tone (2 frets) away from the final Tonic during the 3 to 6.  The VI chord is a Dom.7(#11) while the V chord is a Dom.7(b9) -- which is also a Diminished voicing.  Note that each of the Dominant voicings here are exactly the same chord if played a tritone away.  Try out Mickey's other tritone subs -- making the tritone a min7 or min6 also gives a hip altered dominant sound to the V.  You should also try grabbing a different ii-7 chord to serve as a Dom11 chord for the V.

The basic goal of practicing the content in this PDF is to increase your vocabulary of chord moves for basic building blocks of jazz harmony -- the 2-5, the 3-6-2-5 and the 1-6-2-5.  With study, you will see these progressions again and again in jazz standards.  The extended vocabulary will give you a host of options up and down the neck for playing over these progressions so you are not endlessly repeating yourself comping behind a soloist.  Learning comping is more useful than just learning how to solo with scales or modes -- for starters, you will realistically be comping far more than soloing.  But dig this -- when you start to picture the chord tones of these progressions all over the neck, they will also be the targets you can approach (scalewise, chromatically or any other way) in your solo to outline the harmony.

​My current journey is to get more fluent with diminished chords and the symmetrical diminished scale.  When I see a Diminished 7th chord on a chart, I rarely have anything more up my sleeve then finding the root and climbing an arpeggio.  The sound definitely works but it can get a bit trite, especially over multiple choruses.  The fact that the diminished sound was such a huge part of pioneer Charlie Christian and then the be-boppers, not to mention Barry Harris's Sixth-to-Diminished concept, I've felt the need to visualize the Diminished arpeggios and scales better, at least in one context.

I'm already aware that the diminished sound can be applied with any dominant. The 'half-whole' symmetrical diminished scale can be used from the root of a V to get altered tones, but what about Diminished chords in Bossas or even folk and classic show tunes?

The best I can gather, the Diminished is like connective tissue that links the meat of the Diatonic chords.  Altered sounds on a Five chord is really just a way to lead the ears back to the I chord, often chromatically instead of scale-wise.  When you see a Dim.7 for a whole bar, typcially the same idea is happening -- it is a chromatic walk to the next harmony.  My plan is to get a baseline visualization for any diminished around the Major scale and then adjust accordingly.  My approach -- outlined in the PDF below -- is inspired by the bars in 'Shadow of Your Smile' which moves from Cmaj7 to C#dim7.

My strategy starts on page 1 of the PDF with a set of 'anchors' over the course of the fretboard.  Specifically I am trying to learn a set of 3-note voicings on the middle strings where I tend to gravitate toward when comping.  The voicings are just repeats of two shapes.  Sometimes it is helpful to actually give a name to shapes to aid the memorization -- I'm calling these 'arrow' and 'cup' shapes (the arrow's 'point' is towards the bridge and the cup's 'base' is toward the nut).

The first goals is to learn how these shapes 'sit' against the 'mode boxes' of the fretboard.  I visualize the fretboard by segments where you can vertically play a mode with the mode's root on the sixth string.  I'm learning these 'anchors' by looping two bars of Cmaj7 followed by two bars of Diminished 7.  For each mode-box, I start slow and work up speed alternating between the Major scale and then the arpeggio.  From these anchors I am extending the diminished arpeggio shape out.  The ensuing pages 2-8 show arpeggio shapes for other strings.  As I practice, I'm starting just with the 'corny' arpeggios as a line back to the major scale harmony.  For each segment of the fretboard, I want to visualize the map of these arpeggios over the major scale. 

Page 9 of the PDF begins the rest of the half-whole 'Symmetrical Diminished'. The second 'half' of the scale is rendered for each shape on page 1-8.  The other half of the half-whole scale is the same arpeggio voicings, just one semi-tone up from the anchors.

The 'Symmetrical Diminished' is a synthetic scale comprised of two sets of diminished arpeggios.  Every other note has a semi-tone or whole-tone interval.  The pages 9-16 show what I am calling the 'consonant' half of the scale.  All the notes of the scale one semi-tone up are in the Major scale, save the #5.  Even though #5 is not classically consonant with the major scale, it is okay to resolve on a Maj7#5 chord.  The #5 is consonant in the Barry Harris world.

The arpeggios in pages 1-9 I will call the 'Dysonant' half of the scale.  Even though they have a Perfect Third and Perfect Fifth, you are never going to resolve a Major 7 chord with flat 9 or a flat 7.  These are the same arpeggios in the 'Sixth to Diminished' concept.  They are the diminished arps that alternate between Maj6/min7 voicings to complete the Barry Harris chord scale.

Interesting, the 'Consonant'arpeggios have the voicings you might use for a V7b9 chord.  The major #5 is the b9 of the Dominant chord in a Major key. 

Together, both the 'Consonant' and 'Dysonant' arpegios make up my Symmetrical diminished scale for navigating over a C#o7 from a Cmaj7.  The end goal is to be able to go into this scale at any point, from any point in any Major scale.

Of course this pdf leaves out a third set of diminished arpeggios, which contains the root, the b3, the sixth, and the #11 of the major. These arpeggios lead to other Symmetrical Diminished scales which I am not going into in order to keep things from getting too out of hand. If you think of the 'altered Five' application of the Symmetrical Diminished using the scale in the PDF (the 'anchors' combined plus a semi-tone up) gives you the b9, #9, #11, as well as the root, the third, sixth and the b7 of the Five chord.  The only alteration you are missing is the #5 of the Five.  In the end, in order to play the remaining Symmetrical Diminished scale, you would simply use the 'anchor' voicings in page 1-9 as 'avoid' notes -- avoiding the Major scale's 5, b9, b7 and P3.  In terms of the Five chord, that would mean avoiding the 5, 7, #11, and #3 of the Dominant.

By learning the 'anchors' in page 1 for each mode-box, then learning the other voicings connected to them, then adding the notes a semi-tone up, I hope to get a go-to framework for coming up with diminished sounds relating to the major scale.

This post is inspired by this You Tube video by Jens Larsen: 8 Awesome Types of 3 note Voicings and How To Use Them.

​The zip file below contains a slew of three-note voicings progressing up the neck.

Three note voicing are the Jazz guitar player's go-to for comping.  With three notes against the bass-player's contribution, you can paint harmony that is solid and direct -- using the 3rd, 7th and 5th of a chord -- or more vague -- using 4ths, 9ths, 13ths -- or completely 'out there' -- using altered tones.

Three note voicings also often allow you to have a free finger to decorate or voice-lead the chord with an added line.

By learning the progressions in these pdfs, you will not only have a cool chord run in your pocket, but you will increase your vocabulary of shapes for comping or chord-melody.  While you probably have begun building up your 3-note shapes just by subtracting a note from 4-voice chords, there are other shapes which can be found that don't build up to a four-note voicing.

The voicings on the middle strings (4-3-2) are the most useful, so you may want to start there with each pdf.

Below is an example of Dominant 9 three-note voicings.  The zip download contains several other types, including min-Maj, quartal and cluster triads.

While the CAGED method is a great way to learn all the scale positions on the neck, I was introduced to the fretboard layout from a blues player who taught me about a house with a backyard and a front yard.  I've tried to reproduce the concept here with a story.  Forgive me to those that take offense at traditional cisgender love stories, but it is just a story and not an ideal of how thing are 'supposed' to be.

Below is a kind of map of the Major scale as broken down by 'Mode box.'  The major scale has 7 notes and each note has it's own 'mode.'  The 'mode box' is a vertical layout of the mode's scale when the mode's root falls on the 6th string.  So the 'Ionian box' is the major scale starting on the 6th string.

For this concept, each mode has a landmark on the map.  The Ionian box is some guy's house.  Out front he can see his front yard, the Dorian box.  From the back door, he can see his back yard, which is the Aeolian box.  The Aeolian actually serves as both the front of the girl's house and back of the guy's house.   The girl's house is the Mixolydian box.  The girl also has a backyard, which has a swimming pool.  That's the Phrygian box.  The water's always cold, so it's really a frigid Phrygian box.

Now I'll tell a story.  The protagonist wakes up in his house, the Ionian box.  He goes out back and gets his dog from the backyard.  The dog lives in the Aeolian mode.  From there he goes round to the front yard and gets in his car.  The car is parked in the Dorian box.  Then he drives to his girl's house, which is the Mixolydian mode.  They go out back and go for a swim in her frigid Phrygian box.  The guy says it's too damn cold and decides he's gonna split.  So he goes around front to the Aeloian box and gets in his car sitting in the gal's front yard.  He drives back to his driveway, the Dorian box, then he remembers he forgot his dog.  It's back to the Mixolydian box at the girl's house.  Finally he drives back back to his pad.

What's the point of the story?  Well if you go by the numbers of each mode, the story is a I-VI-II-V-III-VI-II-V-I progression.

Now when I learn the concept of back yard and front yard from the blues player, I'm pretty sure he was telling be the Dorian is the house and the Ionian is the backyard.  In reality, every mode box has a front and back yard.  The back yard has the mode's arpeggio going back to the root on the third string, whereas the front has the arpeggio with roots on the 4th and 2nd strings.  You should know how to navigate the front and back yard of any mode which is why I think this guitarist brought it to my attention.  He saw I was never really going out the back door.

I don't know how much this visualization will help anyone, but I've always thought about these landmarks.  What about the Lydian and Locrian modes?  Well -- aside from the fact they are kind of visually squished in with other demarcations, I see the IV as kind of moving to an adjacent key on the Circle of Fourths -- maybe the Lydian is the next town over.  As for the VII -- that is usually just the 'ii' of the VI.  If you are two-fiving to the VI, that is like a secondary dominant, again -- another key.  I would say the VI is the bar en route to the lady's front yard, or the dog-house out back.

The Sixth-To-Diminished is a chord scale which alternates between Major Sixth Chords and Diminished Chords to provide a chord for every note of the Major scale.  It is just sandwiching a Diminished chord between each inversion of the Major Sixth chord.  If you run up this chord-scale,  you will quickly hear a sound which harkens the chord solos of Wes Montgomery.

Wes Montgomery's octave solos are perhaps the most distinctive part of his sound, but nearly all of his solos were like a three act play:  First, he started with single lines, then he moved to octaves, finally he moved to chords.  Just by the sheer number of strings, he was 'building' up his solo.

There are a few different approaches to chord soloing, most of which involve targeting the note on a chord's highest string as the 'Melody Note' with the bottom strings 'fleshing out' what chord is being stated below.  The Sixth-to-Diminished approach is a quick-and-dirty chord-scale which you can learn on the cheap.

The Sixth-to-Diminished concept is championed by Barry Harris.  I did a blog post on the Barry Harris 'origin' story, but there is no context of what to do with that information.   The  basic takeaway should be that, through these philosophical machinations, the 'Sixth' chord has some interesting 'genes' in its DNA -- specifically related to the Diminished scale.  I imagine early jazzers started heavily exploring the Diminished because they heard the leading tones in an altered functional dominant.

The two-dollar explanation of the sixth-to-diminished is that the chord-scale is continually going from Five-to-One.  As outlined in the PDF, the diminished fingering is really an altered Dominant - a Dom.7b9 chord.  The ensuing chord is the 'One' chord, the Maj6.  Now -- what do jazzers love to do with any harmony?  Take any opportunity to add a 'V to I' cadence.  The Sixth-to-Diminished has the V to I in spades.  Every movement along the chord scale is a V going to a I.  

The beauty of the Maj6 chord is you can easily interpret it as Major or Minor.  Any Maj6 is an inversion of a min7. You may notice that the diminished chords -- spelled out in the chart as Dom.7b9 -- consistently have a note outside the Diatonic Major scale.  The flat-9 of these Dominants are actually the same as a Major#5.  I don't have the complete story on the Barry Harris method, but I know the Maj#5 chord is a big part of it.

If you take a look at the Diatonic chords of the Harmonic Minor, you see the Maj#5 is the Third Mode there.  If we used the Harmonic Minor's Maj#5 as the 'One' chord, the II mode would be the Harmonic Minor's vi  -- Dorian#11.  Let's take a look at the Sixth-to-Diminished harmonization of the II in the PDF.  It shows a Dom.7b9 to the V, but looking from the perspective of the II, we have the Root, the flat third, the sixth, and the #11.  Are the chord tones are outlining the Harmonic Minor starting from the III? Perhaps a discussion for another post.

Below is the the Harmonic Minor Scale and it's diatonic arpeggios.  This PDF is similar to those for the Major Scale and Melodic Minor Scale, so check out those posts if you haven't.  The PDF outlines the Harmonic Minor, it's seven modes and the diatonic arpeggios.

As with the other Scale PDFs, it might be worthwhile to start with the arpeggios for each mode.  Not only are they less notes to focus on, but they are lines in themselves that make succinct, harmonic 'sense' out of the modes.  Once you understand the chord tones for a mode, then you can 'flesh out' the rest of the scale around it.

For the novice jazzer, it is less useful to understand this material for compositional movements, than to just be aware of the arpeggios that are buried within this scale.  While the Harmonic Minor is a great choice for the Min-Maj7 chords and sounds in tunes like Nica's Dream and Nardis, the harmonic minor is probably most used in jazz for altered sounds -- using the Phrygian Dominant over a #11 chord or the Ultra-Locrian for tri-tone colors over a functional Dominant.  Just learning the harmonic scale will give you access to these sounds, but being able to pick out all the arpeggios within it can give you a richer starting point for your lines.

Another key use of the Harmonic Minor in jazz is the 'Barry Harris' approach.  Barry Harris has a whole cosmology of scales and tones that starts with chromatics, splits into diminished and ends with sixth chords.  The 'Barry Harris' scale -- the Major#5 -- is really the third mode of the Harmonic Minor in this PDF.  Check out his 'Sixth-to-Diminished' theory which is at the heart of his teachings.  If you act as if the Third Mode of the Harmonic Minor is the 'One' chord for Major tunes, you can develop a unique perspective into the tunes of the Swing and BeBop era.  Either way, if you are familiar with the arpeggios in the Harmonic Minor and Melodic Minor scales, you will be able to spot them when transcribing the lines of Charlie Parker and other boppers when they go 'outside' the harmony.

​Frank Gambale offered this exercise for playing over chord changes on the 'No Guitar Is Safe' podcast.

Mr. Gambale uses the same strategy so many others use to play over chord changes, which -- in the music he plays -- can come as much as four times in a bar.  The secret is targeting one or two notes in an arpeggio -- essential tones.  The 3rd and 7th intervals are the ones that immediately state the quality of the chord, so that is the obviously place to start.  But being able to get to any interval will help you see the fretboard in a way that lets you play effortlessly over changes.

The Exercise:
Start simple -- looping two bars of E-minor and two bars of G-minor. Play the root 'E' first beat of Emin and Play 'G' on the first beat of G-minor.  Slowly work in the accompanying dorian scale as you feel ready.

From there, target the third of each chord.  Count up the dorian scale tones to the 3rd note from the E for Emin and the 3rd scale tone up from G on Gmin (Hint: you now play G at the start of Emin and Bb at the start of Gmin). Play this note on the first beat of each new chord. Make sure you are finding the equivalent note everywhere in a position, and eventually everywhere on the neck.  The 3rd of a minor is flatted -- it's one fret down from where it appears if the chord were major.

Next, target the flat-7th for each chord.  Loop the four bars and play the 7th on the first beat of each chord, adding notes after it.

From there you can move on to the five, and eventually all the tones, the 9, the 13, the 11. 

If you want to get fancy, target the tone for a specific beat of the chord, or try targeting two non-adjacent tones in a row.

Do the exercise moving two different chords -- Major to Minor, The V Dominant of a Major to the Major, etc.  Find the tones you like for each chord.  Find the tones everywhere on the neck.  After all that has been mastered, find the tones that are 'outside' the scale and know what they are.

Every time you get stuck on a passage of a tune, like a turnaround, break out that chord change and loop it.  Stretch it out and start slow as you can.  Target the 3rd and 7th of each chord.  Next, target all the arpeggio tones, then all the scale tones, finally all the 'altered' tones.  Make sure you are practicing in every position or visualization you have on the neck.

Your voice is the first melodic instrument you probably ever learned, and is the most accessible to the breadth of your audience.  I would argue the more a lead instrument sounds like someone singing, the broader appeal it will have.

I am not a singer and hate singing, BUT -- there are a number of exercises involving singing that will still help with jazz guitar.  Some are more of a time investment than others, where you may feel it takes away from practicing more 'practical' things, but remember that singing is completely portable.  Even just singing around the house washing dishes will keep you creatively developing melodic 'muscles' in your brain.

1) Sing when nobody is around the house or in your car.
Just coming up with melodies when you don't have your guitar is like calisthenics for the melody muscles in your brain.  Imagine a chord or a bar in a standard you are learning and sing a line over it, or come up with a melody and imagine an arpeggiated chord behind it.  Even if you have no idea what chords or notes you are singing, you are still connecting with the art and vibrations of improvisational music.  Or just sing what comes in your brain -- your are still crossing that important bridge from brain to muscle.

2) Sing along to music while it is playing.
Sing along to jazz or even pop music, even if you are just improvising over the harmony.  Try repeating phrases you hear in a solo on the fly.  I like to do this driving to a session -- it's like my first warm-up.  It makes my ear more more acute to what is going on. It exercises your listening muscles.  Listening is as important as anything else playing jazz and singing back a line can give you instant feedback on how acutely you are listening.

3) Sing when you are playing a solo.
Try to sing along with your solo.  This obviously helps with one of singing's biggest rewards: phrasing.  It's not difficult to play sixteenth notes for 32 bars straight without a rest and the fact that you cannot sing along to such a solo should tell you something.  Rests define melody as much as harmonic choices -- they are the 'negative space' that pop the melody out and encapsulate emphasis.  Jazz, not to mention music as a whole, was largely developed by instruments which require human breath.  Musical phrases often 'work' precisely because they emulate phrases of speech from a particular language.  Stewart Copeland likes to explain that even the most complex 12/8 rhythms from the farthest reaches of the world are really just templates of phrases in the local dialect for "I went down to the corner store to buy some milk" or something similar.  Even if it feels dumb, even if you are not playing the same note you singing, even if you are just grunting, even if you have never tried it -- try singing to your solos!  You will be amazed at how your timing suddenly becomes more direct and fluid.  Even non-melodic grunts will give your solo a 'conversational' reference point. 

4) Play a chord, sing a line, play the chord again, play the line.
Even if you know you are going to stumble, do it. It exercises all your jazz muscles.  It will take you out of the visual strategies you've built up eyeing where your fingers should go, what notes go with what chords, etc.  This is something I saw Barney Kessel teach in a video.  It helps build a personal vocabulary.  It gives you lines with 'real' phrasing.  It gives you a fresh and even personal perspective on improvisation over a harmony.

5) Play a note, sing a note, sing an interval of the note, play the interval.
This helps train your ears.  Even if you are getting in the ballpark, you are working your ear, but pay attention to your progress.

6) Transcribe a solo and be able to sing every note.
Transcribing from a master is one of the most beneficial things you can do to help learn the language of jazz.  This helps you really, really learn a solo.  Transcribing it to your voice puts it in your body, not just your fingers.  This exercise will also help you with your phrasing when you play it on guitar.  This is an extreme exercise, but you will get results from it.  When you are able to sing a solo, that solo is part of you, just like all those advertisement jingles and TV themes from your childhood.

You have probably heard someone talk about these exercises before so consider this is just a "blue-moon" reminder.  It will wake up something very deep inside your improvisational ability.  If you are like me, one reason you are playing instrumental guitar music is precisely because you *can't* sing (or rather don't sing well).  Even if you can't sing, don't sing or won't sing, singing will still improve your guitar playing.