Food: Yours, Mine and Ours.
Don’t eat someone else’s food without asking. If you do “borrow” their favorite snack food, tell them and then replace it quickly. In order to keep moochers from accidentally eating your food try writing your name on the containers with a marker. Another way is to assign everyone his or her own food cabinet. This is my preferred method. Choose what works best for the house. As far as condiments go, everyone should chip in; otherwise you’ll have two or three of everything in the fridge and no room for beer and cheese wiz.

Guests or Pests
If you have roommates you can also be sure their significant others and best friends will always be around unless you come up with some house rules for guests. It's one thing to have boyfriends spend the night once a week, it’s another for them to stay every night, eat your food, use your phone, computer and never help with the household chores. This is a major annoyance and must be dealt with before it happens.

The best way to handle the situation is to lay out the ground rules for overnight and weekend guests with your roommates in the pre-nup. Personally, I always feel they can stay over as much as my roommate stays over at their house as long as they're respectful of my space. That means replacing all my snacks they chow down and cleaning up after themselves.

Noise
Be respectful. There’s a time for cranking up the tunes but not every night. Even if your roommates are into it your neighbors may not be. And unless you live in a soundproof apartment or dorm, 10p during the week is a good cutoff time for noise too loud to study or sleep. Midnight on the weekends.