U of Cincinnati law professor Paul Caron of Taxprofblog has a fairly comprehensive roundup of advice for entering law students from a wide range of law professors (myself included), current students, and others here.
I don't endorse all of the advice given, but it's good to get a wide range of perspectives. One last piece of advice, that I think too many law school applicants ignore:
Don't go to law school unless you're fairly sure that you have a real interest in the law or in one of the other professions to which a J.D. is a gateway. There are lots of unhappy lawyers out there who went to law school simply as a kind of default option because they couldn't think of anything better to do. It's no surprise that many such people end up disliking the practice of law. The same point, of course, applies to entering any other profession, but law is particularly susceptible to this problem because of the fact that pretty much anyone who did well as an undergraduate can get into law school. Admission to most other professional schools or PhD programs requires demonstrated competence in specific fields of study or a longstanding interest in the subject in question.
I don't object to people going to law school simply because they want to enter a high-paying profession. But if you go into law primarily to make money, then you should expect that you may not like the work and not be too disappointed if it turns out to be boring or unpleasant.