chors are derived from major scale, in C that is--> c(major 7), d (minor 7), e (sus b9), f (maj 7 #4), g (7), a (minor b6) and b (half diminished). Often used is 2-5-1 progression. --> improvisation on the d-7 is on the second mode from c major scale ...
@IFulcrum hey IF, with all the dominant chords (f7 - c7 is 1th and 5th) i tried f blues scale and it fits great also.On the minor chords i go dorian.