Dear _________: Remind the interviewer of the position for which you were interviewed, as well as the date and place of the interview. It is always courteous to express your appreciation.
Confirm your interest in the opening and in the organization. Highlight your qualifications and slant them toward the various points that the interviewer considered important for the job. If you have done anything since the interview that demonstrates your interest in the position, such as talks with alumni or faculty, research with people or in the library, etc., be sure to mention it.
Include any information not previously presented to supplement your resume, application letter, and the interview. You may have completed a term paper or a research project, or perhaps you have received some kind of recognition. If travel, location, or similar subjects were stressed during the interview, be sure to confirm your willingness to comply with these conditions.
If appropriate, close with a suggestion for further action, such as a desire to have additional interviews at a mutually agreeable place and time. For a prompt response, it often helps to end the letter with a question.