Nomination interview groups can be very diverse as can their questions. I always tell my candidates, foremost, to be themselves. The boards are looking as much, or probably even more so, at how they handle themselves than the exact answers to the questions.
Steer away from politics. If asked a political question about the war in Iraq, the military implements and enforces the policy, they do not make it.
Be prepared to answer why you want a career in the military and why a SA is the best place to prepare for it.
There will usually be a question about why they should pick you. What makes you unique, an ideal candidate?
What concerns you? Are there areas where you feel you may have problems? When I did it, those were my favorite questions. Some were TOO honest, or maybe thorough.
Be comfortable. If you are going to wear a coat and tie, for example, and haven't worn one for awhile, wear it to church a couple of times. Nothing is more distracting than a candidate fidgeting with their tie, cuffs, etc.
Look the person who asked the question in the eye. Take your time. If necessary, have them repeat the question. Buy time if necessary. Formulate an outline before you start talking. Be concise. Don't ramble.
Hopefully, more can chime in with specifics. Good luck.