I'm done with 3 interviews now and feel that I'm eligible to pass on some dough to you ;P. Seriously speaking, it's to express my gratitude to all those resources that helped me in my prep that I'm writing my post.
If you have been active on the blogosphere you wud've read a lot of posts like Xlick's NYU interview prep. report or Hari's tips for interview preparations etc. I don't want to repeat their good advice but just to add my 2 cents to this here I go:
I start my preperations going through the school's website for the (n+1)th time and taking notes of the school's specific activities in my field of interest - let's say entrepreneurship. I try to see if the school has any specific research centers or student-managed funds for use in the specific field, ex.the Wolverine fund of the Ross School. I also try to find info about what intership oppurtunities specific to my field of interest are available at the school. Also, I make a note of the companies that might have tie-ups or for-free projects planned with the schools, the geographical proximity of my dream-companies to the school etc. For ex. someone planning a career in entertainment can choose a college near LA or near NYC. Be sure to mention these points in the answer to 'why MBA' question which is 99.9% probable to come-up in any b-school interview.
Next step is to write down a list of the possible questions that you can expect to be asked. There are hundreds of resources that can help you with this preparations. A few are
1) Clearadmit interview wiki
2) GMATclub's resources like this and this
3) Blogs of current applicants who are going through the same process as you
Now that you have a list of questions, frame your answer to each questions. This part is something that no one can help you with. But you take help from your essays. Also write down a list of your life-enriching experiences - work, personal, academic or community related - and try to see if you can fit in these stories in your answers to the interview questions. Remember - It is on you, and only you, to highlight the different aspects that make you the special person that you are. The interviewer will not ask you specifically if you have you lead your high school team to the state championships, you tell him that to highlight your leadership and sportsmanship.
Last but not the least do a mock interview with a friend or your partner and ask them to be honest in their feedback. They might not tell you specifics about the MBA related topics and answers but they can surely help you with body language and eye contact which , don't forget, are equally important.