This is the No. 1 tip that most people have for getting in to a fraternity -- especially a fraternity that will be a good fit for you. Remember, your fraternity brothers are likely going to be your closest friends in college and probably beyond, so you want them to be guys you genuinely like and have a lot in common with. Pretending to be someone you're not is counterproductive, and nobody likes a fake. Be comfortable being honest with the brothers and they will likely do the same for you.
Brothers will ask you a lot of questions about yourself during the rush process, but make sure you get to know them, too. Not only will asking the brothers questions about themselves show you're really interested in the fraternity, it will help you know if the fraternity is the right fit for you. If you have the opportunity, try to get to know some of the brothers before rush week, as the hectic nature of rush week can make it hard to get to know as many brothers as possible.
Fraternities are more than just party houses, and many of them have minimum GPA requirements and expect their members to work hard before they play hard. Showing that you have what it take to get your studies done is important, and you wouldn't want your GPA to disqualify you. Fraternities will also be interested in what kind of extracurricular activities you do and some demonstration that you will contribute to the community.
Often the key to getting into a fraternity is simply finding the right match. Go to as many houses as you can, get to know the brothers and let them get to know you. You can't make too many assumptions about which fraternity you should get into. Try them out and see which one is the best fit. There may even be more than one that is right for you, and by visiting them both you will have doubled your chances.