Some common chord substitutes used when you have a dominant seven going to its tonic are chords based on the flat 5, the flat 7 and the flat 9 of the dominant 7. For a C7 chord this would give you the chord substitutes F# major, Bb minor, and Db major. Common use of chromatics in jazz are between the 5 and the 6, and between the 1 and the 7 and between 1 and 9. It's also common to substitute a half diminished chord for a II minor chord and lowering the 9 and 6 one half step on the V7 chord when you have a II,V,I progression where the one is either a perfect tonic or a minor tonic. Basically this gives a harmonic minor scale. Hope this helps some.