I would say the single most important thing you can do for interviews is be prepared. Have an idea how you will answer the questions that seem to often come up (Why anesthesia? Why here? Why should we take you?, etc). Have some prepared questions you can ask anybody, even though they are the 8th person that day to ask you, "Do you have any other questions today?" (Yes, what do you consider the strengths and weaknesses of the program? Do you feel the residents and faculty have a good relationship?, etc).
Finally, what I consider may be the most important preparation (unless you are the perfect unblemished candidate), absolutely know for sure in your head how you will answer any questions that make you uncomfortable (Why the leave of absence your 2nd year? So tell me about this DUI? How come you didn't get into an American medical school? You quit surgery after just 4 months; how do we know you won't quit anesthesia after 4 months?, etc).
I bombed my very first med school interview horrendously and barely beat the rejection letter home to my dorm. I just went in as a naive college kid thinking we'd chat and shoot the breeze and it would be a snap. I literally couldn't even answer "Why do you want to be a doctor?" without stumbling around significantly. I never went into an interview totally unprepared like that again, and never had an interview since then even remotely approach the level of just how bad that first interview went. I developed a routine of mentally preparing the night before all of the many future rounds of interviews, and something very stressful actually became pretty easy.
