I played in a mixed league for the first time this summer with my wife as my partner. (Yes -- I realize some people consider this to be a sign of insanity) A few quick observations.
As hard as it seems, try not to treat the female opponent any differently than a male opponent. Use your regular serve and ground strokes. Don't "take it easy" on anyone. Often the women consider this more than a little insulting. But also use common sense -- don't go headhunting or anything.
Expect the male player to be extra agressive at the net and with poaching. It is either because they feel like they need to end points quickly because their partner may be weaker, or they are trying to be macho and show a superior female teammate they can contribute too.
Don't overlook the female player -- I played many matches where the female opponent was the stronger player and it was more effective to isolate the male. Probe both players before you make up your mind about which of the pair to attack.
Expect lobs - lots and lots of lobs. It seemed like the lob was used more than any other shot to try and recover from an attacking shot. Make sure you have discussed with your partner how you intend to handle lobs to particular parts of the court when one or both of you is at the net. I saw too many times when the guy considered himself to be the faster player and would go after lobs that would have been better handled by their teammate.
Along the same lines -- trust your partner to do their job. If you try and play both sides of the net, you will give away tons of points where a ball is hit to the open court you just vacated because you are trying to play every ball.
Mixed can be a lot of fun if you have the right attitude. Oh, and don't berate your spouse/partner in front of your opponents, save it for the car ride home.