A personal statement is basically a "why I should be accepted into law school" essay?
Two major questions you should answer are:
1. "Why you are interested in law school?"
2. "What do you intend to do with your law degree, if it is conferred to you?"
Each of these questions should be substantiated by your experiences, interests and demonstrated abilities (not necessarily in the form of LSAT/GPA, this could include ECs, etc).
The personal statement is essentially an argument for why a law school should accept you. Try to make it interesting, and well, "personal" though. Dryly written personal statements are almost always overlooked or skimmed.