A good way to think of the interview is a live version of your essays. The same questions you wrote about will be asked: why an mba? why now? why <school name>?

I prepped by creating answers for many of the basic questions (based on the theme of my essays) asked and practiced reciting them from memory. I did this out loud because it really helps to solidify the actual speaking part. Also, be wary of reciting too perfectly because it will come off as memorized and canned - if you miss some points and deliver a little off that is just fine.

You can do a search online for sample interview questions - there's a lot of info out there.