Privacy is another area that may be uncomfortable to discuss with your roommate, but this rule can prove very important. Agree that what happens in the room stays in the room – within reason.
Sure, you may not be best friends with your roomie. But you're going to live together in close quarters, and you will most likely know if your roommate has flunked a test, broken up with a significant other or come in a little tipsy. Keep private business private. Agree that you will respect each other and not use personal details about your roommate as fodder for gossip with your other friends.
Most important, don't abuse cell phone cameras and social media at the expense of your roommate. It's easy to snap a picture at an embarrassing moment and share it with others. But what seems funny to you might be humiliating to your roommate. Make a rule and stick to it: Neither of you will violate the confidences that you share, intentionally or otherwise, in your room. And neither of you will post or otherwise broadcast messages or photos about the other without permission.
Of course, if your roommate is breaking the rules the two of you have agreed on, or is otherwise acting in a way that's seriously troubling, you should speak up to someone. But take your problem to your residence advisor or dorm official, not to all your friends and acquaintances.