No matter how well you think you know your friends, living with someone is a completely different story. Before you sign a lease with someone, ask these questions and remember, it will feel like a much bigger deal when you are in the same house or apartment.
1) How clean are you? Would you keep up your end of the deal if we set a cleaning schedule for shared spaces?
2) Do you smoke?
3) How do you feel about overnight guests?
4) Do you have any pets?
5) What kind of hours do you keep?
If you have a problem with your roommate that feels unresolvable, consider mediation. It is a lower cost and less adversarial option than taking them to court.