All the types of substitution you learned in major keys (relative substitutions, scale tone triads or 7ths two degrees ahead in the key, dominant minor, and tritone substitutions) can also be applied to minor keys. The main difference you will find is that when you start to go into the upper extensions of chords built on the harmonic and melodic minors, you will get alterations to the chords. Here are the chords resulting from substituting scale tone 7th chords two ahead for the standard scale tone 7ths of A melodic minor.
This is a solo based on the progression to Black Orpheus by Louis Bonfa. It is in the key of A minor and makes use of many of the chords you now know. The CD also contains a ]am-along version for you to play with. Learn the solo, analyze it and then transpose it to all twelve keys.