This happens less frequently that you might imagine. Most roommate conflicts can be resolved with discussions, compromise and the arbitration of an informed and caring Community Advisor (CA).
Even before you send your son/daughter to college, make him/her aware of the issues involved in sharing space and respecting differences. Make sure your student respects both the private space and the belongings of others.
Advise your student to talk to their roommate via phone or e-mail prior to the time when they actually become roommates. They should discuss which items they will each be bringing to the new shared space. They should also discuss their likes, dislikes, preferences, etc. What time do they go to sleep or arise; are they messy or clean; what time are their classes; do they study often and do they prefer absolute quiet when they study or background noise? As they discuss preferences, each will have a better understanding of how to be respectful of the other.
If issues do arise, advise your son/daughter to have a heart-to-heart discussion with his/her roommate immediately and to be rational, willing to apologize if they are wrong and willing to compromise. If a personal discussion between the roommates does not resolve the conflict, advise your student to talk with their CA. The CAs have been taught ways to facilitate communication, mediate disputes and resolve conflict.
If all else fails, tell your student to request a room change through the Office of Residence Life.