You're serious, eh? First doubles match? What have you been doing all these years, playing nothing but singles?
Sorry for the sarcasm...but it seems a most unusual request.
"Rules" are still the same, just the court size is different. You get the, ah, doubles alleys. You've got to keep track of the serve order but other than that, not much is different...except in strategy and execution. Be prepared for much shorter points, coming to...and winning at net (rather than from the baseline). Communication with your partner is key. And generally speaking, it's a lot more "fun" than singles.
Good luck and keep us posted.