Format the letter in a professional style. Write it on letterhead, if possible. Include your information in the top left corner in block format. The information should include your name, your address, your phone number and your email address. Create a space below this block of text and the salutation.
Introduce yourself and your relationship to the person on behalf of whom you're writing the letter. Spend no more than three sentence on this, but make sure it clearly shows you are an expert in your field and you know the applicant's strengths well.
Write two or three block paragraphs discussing the applicant's strengths. Give concrete reasons for recommending the applicant. These reasons should include a discussion of the applicant's strength in comparison to others. For example, you might say that the applicant consistently wins in class debate against other students.
End with the word "Sincerely" and three or four spaces. Type your legal name. Print the letter and sign your name between the salutation and your name.