a current student here
Your MaineCard is your life up at the school. Not only does it allow access to your dorm hall and dorm room, it's also your key into other dorm halls and the dining facilities, and carries Black Bear Bucks and Dining Dollars that you put on it. Never leave your room, let alone your building without it. I personally have a habit of checking that I have it every few minutes walking around.
Find out when the activities fair is: there's a day in the opening week of the Fall semester where almost every group on campus is on the mall in front of the library with a booth set up so people can go check them out and get put on an emailing list.
The walls of the dorms are relatively thin. Keep conversations on Skype or w/e down if you want them to be private, and bedsprings bouncing can be heard in the adjacent rooms, so please don't blast music or have movies playing at 1 in the morning.