As an attendee, I think my biggest advice would be to arrive early. A lot of the adcom members get there early and its a great opportunity to chat informally without other people waiting behind you to talk with that person!
Also, don't ignore any adcom members - Don't just try to talk to the Dean or the Director to make an impression. I think its just as important to talk to every member and any alumni or current students there to really get a feel for the program.
Dress professionally. I think first impressions are huge. If this is your first time meeting the school and potential class mates, dress for success. You'd be surprised how many people come in jeans, shorts and a t-shirt.
Network with your competition... urr classmates. Get to know them, why they're looking into bschool, how the essays are going for them, etc.
Follow-up. If you had a great conversation with one of the adcom members, shoot an email thanking them for their time. If it was just a casual quick conversation... maybe not so much.