Review any agreements that you and your roommate have signed. FindLaw.com says you will need to know how much notice you must give your roommate and landlord, as well as whether you will face any monetary penalties for breaching the agreement.
Prepare and evaluate a list of reasons for ending the roommate relationship. Be objective and fair in your assessment; don't make personal attacks on your roommate.
Talk with your roommate in person. Although you may wish to present your roommate with a formal written statement ending your relationship, discuss the issue face-to-face. This will give your roommate a chance to ask any questions and clarify what steps each of you will be taking to find a new living arrangement.
Determine the terms under which you plan to leave or to ask your roommate to leave. Unless it is specifically outlined in a lease or roommate agreement, talk to her about an appropriate timeframe. If you are asking your roommate to move out, give her at least 30 days notice, St. John's University in Queens, N.Y., advises in its website.