I just had my interview today, and I would say try to prepare for the basics, like high school experiences, leadership roles, and motivation for becoming an officer. Reread your resume and essay because some questions will pertain to them and you don't want to give contradicting or unsimilar answers. But also, don't prepare so much that the answers sound canned. That'll come off as insincere. Don't wing it, though,have an idea of what's going to happen. Plus, by having to think on your feet for an answer a little bit, you'll be more personable, and that's really what the interview is all about. Good luck!