Some of the other guys can answer this a lot better than I can, but I'll give it a shot.
Look at Mickey Baker's lesson 15. "Bridges," he's talking about, and how to jazz up the "standard" chords.
Say you want to play the first bridge, the 2 bars each of E7, A7, D7, G7. You need to know what chords the piano player is playing. If he's playing the standard chords (above), you're okay with most of Mickey's substitution suggestions. But you don't want to play that G13b5b9 chord, if piano man is playing a plain old G7 (which might have a 5th - a D note - ringing out against your D flat note... the "b5" in the G13b5b9 chord that Mickey suggests.)
For chords like Dm9, Dm7, Dm6 -- these work in place of a D minor, because these "color" tones (9, 7, & 6) are in the same scale the D minor comes from. When he tells you to play, say, a Bm7 & E7, two beats each, over what's normally four beats of E7, you're making a "ii-V" out of a whole bar of just "V"... jazzing it up, adding movement and color.
Whoa! I just realized how much stuff I somehow know but can't quickly explain. The Mickey Baker book is probably a "must-have" for learning what you're doing. However, he doesn't do much of a job of explaining the "whys" of his suggestions, which is what you seem to be needing to know, so you can play in your group and not clash with the piano player's stuff.
So: these other guys on the forum can explain better. Meanwhile, I suggest you get yourself a copy of Jody Fisher's _The Complete Jazz Guitar Method_. This is a four-volume deal, and if possible, you can do yourself a favor by buying only the first two volumes (for now anyway.) Here you'll learn the chord & scale theory you must know to understand and play jazz.
AND: you'll probably find good info about this at Matt Warnock's great website, which I think is:
Matt Warnock : Jazz Guitar, Guitar Lessons & Guitar Journalism | MattWarnockGuitar.com
Best of luck!
kj