Take advantage of the Add/Drop period, especially during freshman year. If you aren't sure about a class, sign up and try it out for a few days.
Get a windproof umbrella - the top of the hill gets gusty.
Wander through Gantcher in your spare time - there are super cool secret rooms (the squash courts have a trampoline room)
If you are from a place where it doesn't get very cold (like Florida) find someone from Canada or North Dakota and take them shopping with you. They will be able to teach you how to dress during winter.
You can check when the dining halls will have your favorite food online.
If you're a musician, take advantage of the World Music Room on campus, which houses hundreds of instruments from around the globe.
Bring a sled, and you will instantly become the coolest kid on campus
http://www.raptorattack.com/tufts_courses/ is a great way to plan out potential schedules and look at the awesome classes you can take!
Go to office hours. Especially in a giant intro class, and if you want to be one of a handful of kids that your professor knows on a first name basis.