Be social. You certainly don't need to do everything together or be the best of friends -- but hiding out in your room all the time and declining every time your roommates invite you to do something sends a negative message.
Part of what can make living with roommates fun is hanging out together. Likewise, don't form a clique and exclude another roommate from activities. If a roommate situation is not working out, address it directly.
Share decorating space. That means you should all get equal wall space (if you want it) to hang art in common areas, and you should work together to decide on furniture arrangements and accessories. To each his or her own in bedrooms, but shared space really should be shared.
When you move in, it can be a fun bonding experience to tackle a household project together. Hit the local flea market together, paint a piece of furniture, or collaborate on an art wall.
When you are done with something, put it back. Just because your roommate seems to always leave her stuff laying around doesn't mean you should, too. Especially in households with three or more roommates, messiness is a slippery slope. Set a good example, and it's more likely your roommates will follow suit.
The best way to avoid conflict around food is to agree early on how you will handle groceries, and stick to it. Here are three common ways to handle the food situation, along with pros and cons:
- Share everything. For some, sharing food and splitting costs evenly works out without a hassle. Conflicts can arise if one of you has friends over a lot and feeds said friends from the (supposedly) equally shared food stash. If you go this route, be clear that the food is for roommates only.
- Separate sides of the fridge. Shop separately, and keep your paws off your roommate's food. This can be a smart choice if you tend to buy very different kinds of food (i.e., one roommate is vegan, another loves meat).
- Share staples, split the rest. This compromise sounds good, but can be a little tricky in practice. Be sure you agree on what exactly is on your list of staples, and trade off paying for them.
Set up a chore chart somewhere easily viewed by all housemates, and use it to rotate tasks. Common courtesy dictates that each person should pull his or her own hair from the drain after showers, and replace the soap or TP if you use the last of it.
Make things easier on yourselves by setting up a single spot where mail always lands as soon as you walk in the door.
Make a spot for keys and a charging station for devices, and you won't lose them either.
If your roommate has been taking your stuff without asking, have a conversation with her about it as soon as possible. She may have just assumed it was OK with you, so be clear about how and what you are willing (or not willing) to share. And be honest: If you regularly borrow your roomie's shoes, don't get your feathers in a ruffle when she borrows your sweater.