Can't really go wrong with chord tones.
If you look at them as scales rather than chords, there are lots of common notes, identify them for a start.
D minor - D, E, F, G, A, Bb, C, D
C minor - C, D, Eb, F, G, Ab, Bb, C
G minor - G, A, Bb, C, D, Eb, F, G
Just record the 3 chords, and practice soloing over them, play safe to start, then start experimenting. If you come across something that sounds cool, look see what it is, and remember it.