Cool, calm, collected. Know your stuff on current medical topics (healtcare issues). More important than what you say though, perhaps, is how you say it. Don't appear razzeled, no matter the question.
As for how best to prepare, everyone has their own individual ways on how to prepare for the current events/medical topics, but I'm pretty sure everyone would suggest the same thing for info about the school: SDN interview feedback and the school's website.