Mutual agreement at the beginning can avoid many problems in the future. If your roommate doesn't pay the rent, you are legally responsible for their portion of the rent. If your roommate flunks out of school, you will be stuck with their rent or stuck finding a sublessee. If you are a teetotaler and your roommate is a party animal, conflict is inevitable. If these habits are evident before you sign a lease, there is no reason to believe that they will change come August.
Some people have trouble lending out stuff at all so be sensitive.
At some point, if your roommate is like most people, he or she will be angry, hurt or frustrated, or simply in a bad mood. A relationship break-up, an incident at work or a bad grade can cause emotions to flare. Allowing your roommate time to calm down and deal with his or her problems can prevent making things worse and will help build a stronger relationship between you. It is advisable to write down the agreements you and your roommates come to regarding your living arrangements. The Students' Legal Assistance Office, located on the sixth floor of Holmes Student Center, has a form available called Roommate Agreement for this purpose.