Get to know your roommate(s). He or she is going to be the person you're likely to see the most, so it's crucial that you can at least peacefully co-exist, if not become friends. This can be extremely challenging for those who haven't had to share a room before, but it's very doable with a little patience and understanding. While you and your roommate might be complete opposites, it's not unheard of that you could also become lifelong friends. Find out their likes and dislikes, hopes, dreams and goals. While you're doing this, set boundaries from the beginning. Agree to give each other your quiet time and your personal space, but also set up times when you can do things together. Sometimes sharing a meal in the cafeteria and providing a sympathetic ear to academic difficulties can bring two people a lot closer together.
Make sure you've brought all the necessities; if you haven't brought them from home, make a trip to the store soon after moving in. There's nothing that will make you feel uncomfortable in a new place than not having something crucial like clean towels or a toothbrush. Most colleges will send you information on your roommate including name, hometown and phone number ahead of time. If possible, get in touch with your future roommate before you even move to see who's going to bring the big items that you can easily share, such as a refrigerator and microwave.
Make your dorm room yours. Don't just leave your walls blank and your bookshelves filled only with textbooks. Bring some of your posters and decorations from home, but use this opportunity to shop for some new things, too. Every college town has stores that sell everything from posters and tapestries to door beads and lava lamps.
Meet your RA, and give them the same chance you give your roommate. For the whole semester--if not the whole year--your RA is going to be the authority figure on your floor, responsible for keeping everyone safe and sane. They're there to help you with your problems and help in case of conflict, but they're students just like the rest of the floor.
Take some meals in the cafeteria. Even if you don't know anyone or don't have anyone to sit with, grab a tray and take a seat. Studying in the cafeteria is fine, if not difficult, but for the first meals leave your books in your room. People will be more hesitant to approach you if you look like you're deep in your studies.
Find out what activities your residence hall offers. Many have TV lounges or game rooms, and these can be great places to meet new people. If your hall has clubs or groups, consider joining. This goes for other campus activities, too. Once you're settled in your room, take the opportunity to look for bulletin and notice boards to see what's posted.
Explore outside your dorm room. Sometimes you're just going to need to get away for some fresh air, whether your room is being monopolized by your roommate and their significant other or there's a party down the hall. Find some places where you can go for some peace and quiet, whether it's the computer lab, the campus library, a coffee shop down the street or some hiking trails. Having a retreat that is all your own can save not only your sanity, but your relationship with those you live with.
Remember to be courteous to not just those you share a room with, but those on the floor as well. Dorm walls are usually thin, and the sounds of a stereo or loud TV carry well. Don't throw in a load of laundry and then forget about it. If someone does overstep their bounds, be polite when you ask them to do otherwise; always remember what it would be like to be in their position.
Find out what classes and majors people are taking. There's a good chance that you'll share some classes with other people on your floor, or find that someone else has already taken the class that you're having trouble with now. There's few better study partners than the one living a few doors down, and the English major struggling with a math class will probably be more than happy to proofread a paper in exchange for a crash course in Calculus.