The focus of a B-school interview can range from specific questions about your job to broad discussions on life. Approach the interview as a conversation to be enjoyed, not as a question-and-answer ordeal. It may be about your hobbies - your recent cross-country trip. This doesn't mean that the interviewers are not serious. It just means that you're being sized up as a person and a future professional in all your dimensions.
Try to be your witty, charming, natural self. Donot try to put on. The interviewers will be able to see your masks through. Students, faculty, admissions personnel and alumni conduct interviews. Don't dismiss students as the lightweights.
It is important to have a good idea of "What you consider to be your greatest strength, why and what are some examples that show this", before you go into an interview. Although the interviewer will most likely ask some pointed questions, you may also encounter something as broad as "So, tell me about yourself." These open ended questions are usually the ones that help you lead the interview.
Either way, you should have in mind what you want to convey about who you are before you go into any interview. Lack of preparation is a common complaint among interviewers, and if you are prepared, you will stand out among your competitors.