Watch the Melodic Minor Substitutions online guitar lesson by John Stowell from Modern Jazz Improv

Notice that I'm using melodic minor chords in the four keys as altered dominant chords (i.e., C#, Bb, F and G melodic minor chords as C7 altered). A melodic minor chord utilizes the following intervals: I-b3-5-6-7-9-11-13, and sometimes I'll create a chord that draws on both the original dominant chord and the melodic minor substitution (i.e., C#mimaj9/G as C7 altered). Eventually all of these layered substitutions become part of a larger picture of how you articulate tensions/resolutions over dominant chords.