Here is what I did. Schools request some specifics such as being signed, being on official letterhead, and including the applicant's full name and AMCAS number. If you are requesting a letter before you have an Amcas number then that oculd be hard to include. Everything else you should specify in your request.
5th May, 2012
Dear
.
I am writing to you in request of support for my medical school application in the form of a Letter of Recommendation.
I have attached a rough draft of my personal statement that I will be submitting with my application to give you some more background on where I see myself in life and what I am hoping to achieve.
With the time that I spent with you
.. in work, volunteering, whatever
.. I hope that you are able to provide a positive contribution to my admissions package. More discussion of our relationship, what I learned from you, what I learned about myself. This helps the letter writer select some topics to write about. Help them help you.
I request that the Letter of Recommendation be forwarded to the online letter-service, Interfolio. Please address your letter on official school letterhead and include your signature. I have included the Interfolio Document Request form which must be included with your letter of support when posted to Interfolio. I have provided a pre-stamped and addressed envelope along with a copy of the Writing Letters of Recommendation guide from University of SDN. If possible I would appreciate receipt of the letter by July 30th, 2012.
The official letter must include the following identification data in order to be linked to my application:
Jane Mcgruber Doe
AAMC# 12345679
I thank you in advance for your help and please contact me with any and all questions either via email sdner@sdn.org or phone 123-456-7890.
Your Sincerely,
Jane Mcgruber Doe