Start the letter. Place your name and contact information at the top of the letter. Begin the document with "Dear Admissions Committee:."
Express your interest in the institution. The first paragraph should be a passionate statement about why you wish to attend the school. Keep the paragraph concise; however, be sure to really convey your desire.
Express the rationale for the waiver proposal. Some good reasons include illness, death in the family, duration of time between your GPA and the application, adversity, disablement or other extenuating circumstances. If you have documentation, attach it to the letter.
Thank the committee for its time. Conclude the letter with "Sincerely" followed by your name. Physically sign the letter.