I'm trying to make sense of how to navigate a minor ii-V-i.  The first confusing thing is there are three minor scales:

• Natural Minor
• Harmonic Minor
• Melodic Minor

First I need to get these minors straight!

Natural Minor

• same as Aeolian mode
• has all notes of the major scale
• is the sixth degree of the major scale
• its arpeggio has the same notes as a C6 arpeggio
• has all the notes of the min7b5 arpeggio
• has a flat seven
• has a flat 13 (flat 6), which is the b9 of the V chord

Harmonic Minor

• has a Major 7 (only difference from Natural/Aeolian)
• has the two fret 'gap' between the M7 and b13
• has a flat 13, which is the b9 of the V chord
• has the flat 5, and all the notes of a min7b5 arpeggio

Melodic Minor

• has a Major 7 (only difference from the Dorian mode)
• it is also the same as a Major scale with a b3
• the seventh mode of this scale is known as the 'Altered' Scale (good for Altered Dominants)
• Has a Perfect 13 (P6), which means no b9 for an Altered Dominant
  
• does not have b5 of the min7b5 chord, so bad for half-diminished
• best suited for Minor/Major chords or Minor 6 chords

In light of this, Harmonic minor works very nicely for the ii-min7b5 and the V7b9, while the Melodic minor works well at Major-minor tonic resolution.

The other approach is to use the second mode of the Harmonic minor for the ii chord and then use the Altered Scale (7th mode of the Melodic minor) for the Altered Dominant V chord, then return to the Melodic minor for the tonic.

In the first approach, there is only one note that is really differing -- the tonic's b13 moves to the Perfect 13.

The second approach is a bit more difficult because you are moving the same scale around and then back.  Quite a number of notes are changing only for one measure or half a measure.

A while ago, I began to learn how to superimpose the Altered scale of the V over all the Major mode boxes, but that knowledge is out the window for a minor ii-V.

If you know that a minor key is the 6th of the major, then you'd think it would follow that the minor progression would essentially be a vii-iii-vi progression.  This is not the case.  The minor progression is 'harmonized' through the Harmonic minor scale. When you build chords off the Harmonic minor, the iii is really a Dominant -- the 'iii' is really a Dominant. 

This means, if you are trying to picture the minor key as the sixth of a major, the root-6 Altered scale for the V is going to be where the Phrygian is, instead of where the Mixolydian would be.

Instead, you have to picture a whole new set of mode boxes on your fretboard -- that of the Harmonic minor -- and then figure out how the Altered scale (or the melodic minor moved one fret up) goes on top of that!  That's a lot of mental gymnastics!

It is probably a good idea to be able to picture various modes of the Harmonic minor for a key.  More importantly, it is good to know your arpeggios and what notes around those notes cause the most tension and which notes are avoid notes.  You probably want to avoid the b9 of the tonic.  

The Harmonic minor will be good to learn up and down the neck. Did you know all the notes of a Dominant 7 arpeggio are in the third mode of the melodic minor as well as the fifth mode?

If you calculate a 'diatonic exchange rate' for the minor ii-V-i, you see that the b13 of the minor tonic is the b9 of the V chord.  Similarly, the b13 of the minor tonic is also the b5 of the ii chord, so it is a great note to hit over a minor ii-V.

I'm going to focus on using the Harmonic minor over minor ii-V's and practice picturing how they sit over the Natural minor scale (Aeolian mode) across all my mode boxes.  Then I would feel more confident about shifting to the Altered scale for my dominant.

Below I tried to illustrate where the notes are on all three minors, visualizing through the root-6 mode boxes.

 I'm really digging this you tube lesson by Jens Larsen, which is a cool introduction to chord soloing.  He has a few others on the subject on his channel.

What Jens has done is taken all the notes of C major on the 'B' string and 'harmonized' three-note voicings for D-7, G7, Cmaj and A7b9. Another lesson shows the same concept formatted for F major, with additional chords to navigate the high 'E' string.  I've diagrammed both to visualize on the fretboard in the PDF.

Taking the C major example:  For the G7 'chord-scale', every note in Cmajor on the 'B' string has a corresponding three-note voicing -- that's the high note with the green box around it in my diagram.  The remaining two notes of each voicing (on the 'G' and 'D' string) will ideally have one or more 'Essential Chord Tones' for the G7 chord.  For G7, the ECT's are the root, the 3rd and the flat-7.  Occasionally these notes are not available, so the voicing is 'shoehorned' in using other nearby notes from the Cmajor scale, which also make sense in a G7 arpeggio, like a 5th or a 9 or a 13.  These chord scales can be used to play 'melodies' on the B-string over a changing chord pattern, like a C major turnaround.

My strategy for learning and applying this stuff for the Cmaj turnaround has gone like this:

1) First, I need to know all the notes of Cmaj on the B-string.  I set up the turnaround -- Cmaj7 / A7b9 / D-7 / G7 -- in a loop and practice making turnaround licks -- playing only on the 'B' string.  After a while I started practicing octaves to drill the idea home more, thinking about the top note on the 'B' string as the 'melody' note.

2) Next I systematically learned each 'chord-scale' by rote.  I learn this scale with the same strategies as any other scale.  First learn to play it up the neck, then down the neck.  Then I start skipping around in systematic ways, like play the first voicing, then the third, then the second, then the fourth, etc.  When I'm learning the scale, I'm constantly reminding myself "This is the D-7 chord scale" and try and pick out roots and ECTs as I move.

3) After that I made a backing loop for one chord and moved up and down the corresponding scale freely improvising.  I started to get a feel where the ECTs were for each chord.  I would also occasionally hang on a voicing and try and locate where I was on the Cmajor scale, playing other surrounding notes in C major to make sure I had a picture of that scale underneath my voicing.

4) Next I plugged in the the same turnaround into my iReal software, except with enough measures on each chord to systematically do the chord-scale in both directions.

5) At this point, I felt ready to tackle some of the turnaround examples in the lessons Jens provided.

6) Finally I began to noodle around in the same way as in step 1, except instead of playing an octave, I was playing a chord-scale triad from whatever chord I was on.  If I felt I was getting ahead of myself, I would go back to the other steps to make sure I knew all the voicings and could shift between chord-scales.

It's been a blast playing these chord-scales over the turnaround.  I began to get a feel for which voicings are 'passing-chords' and which are better to land on.  Soon, I'm going to check out the other video lessons by Jens and learn voicings he constructed for F major, including voicings for the high 'E' string.  After that, I'm going to start moving to other keys and maybe try constructing chord-voicings for minor turnarounds.

I made this chart to highlight the Essential Chord Tones (ECTs) for each chord in a diatonic progression relative to the numbers in the Key scale (Ionian Major).  My shorthand for this concept is the "Diatonic Exchange Rate." 

When you play the root of the ii chord, you are just playing the second note of the Key scale.  The third of the ii chord is simply the 4 of the Key scale.  If you think of just these number for each chord in the progression, you can focus on the intervals of the Major scale instead of thinking about arpeggios relative to the Major scale.

I thought this might be helpful to come back to in light of chord solos.  In a chord solo, we have a melody, say on the 'B' string.  For each note we want to accompany with a chord, we have to find at least one ECT common to the chord for the rest of our fingers.  For a ii chord, we would really implicate a minor strongest if we have the flat 3rd of the ii.  Instead of finding the root of the ii and then finding its b3, I would rather just go directly to that note, which happens to simply be the 4 of whatever key I'm in. 

The chords are ordered in 4ths/5ths, common to progressions in Western music.  If you go bottom to top, you are moving in 4ths.

On the second page I grouped the ECTs in order of precedence.  Minors differentiate themselves from Major by virtue of the b3, where as Dominants differentiate by the b7.  You will see a pattern here: moving in 4ths, the third is the seven of the next chord in the sequence.

In the PDF below, I have diagrammed the arpeggios in each 'mode box' for diatonic chords with the 'diatonic exchange rate' pasted on each note.  I excluded the IVmaj7 on the first page for room, but it is diagrammed on page 5.  I also added some extra diagrams for altered dominants.