I met with a Dean from a school that is located pretty far away from where I live. It was more of a conversation than an interview, but I'm sure this could differ based on the personality of the person you speak with. I would learn as much as possible about the school - curriculum, clinics, special programs that make them unique, etc. Make a list of questions that you can ask, stuff that you couldn't find out yourself online that will show that you really researched the school. You want them to know that you appreciate what they have to offer without being desperate. As for what to wear, it's DC, so don't worry about looking pompous! Just don't act pompous and you should be fine. I talked to someone on the admissions staff and they said that visiting is really the best thing you can do because they can associate a real person with a file. Have you talked to the admissions office about how their numbers are? A lot of schools have already done a second round of deposits and have a better idea of the odds of actually using the waitlist. Good luck with your meeting!