A few guidelines I would recommend (and this is not necessarily true for all women):
1) Avoid locker room style talk. I know a large number of women that are put off by discussions of male parts, references to male parts, "is she hot?" type comments, or slang references to female parts (calling people a "c**t", or talking about "t*ts and a**").
2) Avoid using the tired expression "Girl gamers are always either ugly or taken". This can only backfire on you if they happen to be attractive by your standards and not taken. It's also been heard by every experienced girl gamer probably at least 10 times.
3) Avoid hitting on us. We're here to game, not to find a romantic partner. If, after several sessions of the game, you suggest getting a cup of coffee or going out to a bar (assuming that we're of age and all that)... that would be FAR more welcome. Get to know us first. Also, pay attention to rings on fingers. Married women don't want to date (generally speaking), and neither do lesbians.
4) Don't be intimidated by us and don't coddle us. Most of the time, we're just as serious about gaming as you. If we're a new player, we're new like any male player. If we're an experienced player, we'll be insulted by coddling just like an experienced male player would be.
