always come prepared to any events where adcom and/or students will be present. bring a resume just in case, but dont pull it out unless they ask to see it.
if your visit includes a class session, dont raise your hand during class no matter how good the question is.
dont come off as creepy or weird. usually when applicants are in the early stages of the b-school app process, they want to come off as worldly, intelligent, driven, passionate, etc. however, when they go to talk to adcom members, they come off as... the opposite. just be yourself and make sure you have reasons as to why you want to attend the school.
if there are a bunch of people on line waiting to talk to an adcom member, dont monopolize his/her time. just give them your 30 second pitch, make one or 2 points, and ask if you can email them in the future with any specific questions.
if there aren't a ton of people, try and have a conversation with them. dont just ask them 100 questions - that doesn't really accomplish a lot.