Agree on Shared and Personal Possessions
Space in the dorm is very limited and so are students' budgets. One solution to both problems is for roommates to bring or buy items to share. Between your table lamp and curtain and your roommate's microwave oven and dishes, you can furnish your dorm at a considerable savings. Some roommates share responsibilities for common needs: One person buys the laundry detergent; the other supplies the quarters for the washing machines.
By the same token, it's a good idea to specify which items are personal property. Views on what's personal and what isn't vary. Don't assume your roommate knows your printer is off limits, for example. Ask before using a roommate's things, unless you're sure they're meant to be shared.
You don't want to be unreasonable, of course. Make exceptions for emergencies. Do you want your roommate waking you at 1 a.m. to ask to use your printer for a term paper that's due at 8 a.m.?
You might want to put your name on your things, whether those things are private or shared. This will prevent problems when you and you roommate part ways.