Although Brazilian Jiu Jitsu is a male dominated sport - and will be for the foreseeable future - the female population is still quite significant, and growing rapidly. Odds are you will train with a woman or girl at some point in your early career. Here's a little cheat sheet of things to do... and not to do...
Remember the size-strength differential
Most men who train jiu jitsu are generally bigger and stronger than the women on the mat. And even if they do happen to be the same size, a man will still be far stronger than a woman... by two and sometimes three-fold. That's just a fact. This is why women tend to pick up technique at a faster pace. They basically have no choice. They can't rely on strength to get them through challenging situations, whereas a man in the same situation might be able to blow out of a submission or force a sweep. For the most part, jiu jitsu enables a smaller, weaker person to prevail over a bigger, stronger opponent, but when both parties have an understanding of jiu jitsu, the odds often tilt again in favor of the stronger opponent. So remember, when you're getting your butt handed to you by someone of the "fairer" sex... yes, you can hulk out of a submission or overpower her technical attacks, but it will neither do your nor her jiu jitsu any good.
Treat her with the same respect you would a male training partner
There is an hierarchy in jiu jitsu, and your belt color indicates where you are in it. The most important thing to understand is that your level in jiu jitsu is determined by how much knowledge you've acquired... not by how many people you've tapped. That female purple belt in the academy has just as much experience and knowledge as that male purple belt. So be conscious of how you treat her and what you say to her. Would you do the same with a male purple belt? If the answer is no, just don't do it. For example, you wouldn't say "good job" to a higher ranked male training partner and risk sounding condescending? Probably not. So don't say it to a higher ranked female training partner.
Keep the drama off the mat
When you put a bunch of people with shared passion together, it's just natural that sparks will fly somewhere in the mix. We're only human. But it's not cool to act on those feelings while you're still on the mat. Whether you're testing the waters to see if she's interested, already in the midst of a steamy romance, or you're in a full-blown tiff with your significant other... keep it off the mat. The mat is where you and your teammates go to learn, train, and often to get away from whatever craziness life is throwing at them. The last thing they need is for "crazy" to infiltrate their sanctuary. Not only that, but if said woman does not reciprocate your feelings, you may make things very awkward for her if, or when, she has to partner with you.
Especially if you're a lower belt, your female training partner has a lot to offer you. As I mentioned before, she will likely be far more technical than many male training partners, because she has never had the luxury of strength to compensate for any lack in technique. As long as you treat her with respect and as a fellow teammate, and as long as you be conscious of your size and strength relative to hers, you'll find she will be one of the greatest resources in your own jiu jitsu journey.
Train on. Oss.