The most important thing is to TALK about what is bothering you. Talk about the small things that bug you before they become big things.
If you don’t let your roommate know that something bothers you, she/he will continue to do it. So, if you don’t talk about it, then you have to let it go.
If you are crazy about cleaning, set a cleaning day for yourself. You can’t control your roommate, but you can control your own actions.
If you are the messy person, keep your crap out of your roommate’s way.
Good rule of thumb: if you are done with the food, throw it away right away.
Showering at the same time everyday should prevent from fighting over the shower.
Head phones are beautiful. Ask your roommate before blasting music, especially if your roommate is doing homework.
If your roommate is doing homework or trying to sleep, don’t bring visitors back to your room.
As far as boyfriends/girlfriends, a dorm room is small enough without your SO moving in too. An SO probably shouldn’t stay over more than two or three times a week. And when your roommate is in the room, you and your SO shouldn’t escalate past kissing.
If one of you is trying to sleep and the other one needs to do homework, the one doing homework should go into the hall or the library or a study lounge. Finding a secondary location that you feel comfortable in will help ease tension if you need time away from your roommate. (I’m not talking about finding a boyfriend/girlfriend for the sake of using their room).
Be clear about personal belongings. It’s uncomfortable to talk about, but you have to do it, and things will run a lot smoother if you do it.