Roommate Wars, How to avoid them.

Roommate disagreements happen. Even among the best of friends. The best way to avoid roommate disagreements is to get everything in writing. Ok. You can't think of everything. But up front, even before you move in, get as much as possible written down.
Finances first. Who pays what and for what. House rules, that's housekeeping, i.e. who cleans what and when. These can be printed and posted. Usually that is in the kitchen and the bathroom. These are the "common" areas where the most common problems occur.

Stay over rules are something else again. Whose friend(s) and when. And when does a guest become another roommate.

You're thinking,"Yeah like this is practical". Well, no, you just can't think of everything that might come up. And no one ever thinks they will have a disagreement with their friend. But. Here are the two most common areas of human disagreement. Love and money. Yup. I'll bet if you think back to the major and minor disagreements of you life. They were about either love or money. The rules of love aren't generally written down. But. Money can be determined and divided up easily.

So to keep a roommate as a friend get stuff in writing. If you've already moved in and especially if "stuff " is coming up take some time to talk about it now. Now, before disagreements become a war. And there are no winners in that one.