Living in a dorm turned out much better than I expected. I never had to share a room before but was fortunate to know my roommate in advance. It's important to discuss "rules" for the room. For example, having friends/boyfriends over, falling asleep with tv on, etc. Living in a dorm can be a wonderful experience because you get a chance to make friendships outside of the classroom. These bonds can last a lifetime. You do have to be cautious that you may be sharing a bathroom with many people and they may not have the same expectation of what's "clean". Also, sometimes it can be a bit noisy but if that bothers you than invest in good headphones. :)
Overall, it's an exciting experience so soak it all up and enjoy it.