Who should you ask?
It is important that your recommenders know you well, think highly of your work, and are able to write a thoughtful and informative letter of recommendation on your behalf. Consider the purposes for which you'll want to use letters of recommendation and try to include recommendations from people who have worked with you in academic, clinical, research, extra-curricular, athletic, and/or professional experiences relevant to medical school. Generally, character references from people with whom you have not worked, such as old family friends, are not particularly helpful.
When should you ask?
It is essential that you make your request of your recommenders as much in advance as possible. Faculty members especially receive many requests to this end, so please allow for at least 4-6 weeks' time for them to write your letter of recommendation. This will also allow for some follow-up time after you make your request.
How should you ask?
You always want to make sure that anyone who recommends you is happy and willing to do so. We recommend that you phrase your request in such a way that, if someone does not feel comfortable writing for you, he/she can gracefully decline. Pressuring someone to write a letter of recommendation for you is likely to result in a lukewarm or qualified recommendation which ultimately might do more harm than good.
Letters of recommendation are most effective when they can describe you as well-suited to a particular goal. To that end, we strongly suggest that you have a conversation with your recommender - in person, preferably, but over the phone is also okay - so that he/she can refamiliarlize him/herself with you and your strengths, goals, and overall personality. During this conversation, it may also be appropriate to remind your recommender of your background; providing an updated resume or some graded work from his/her class are good ways to do so.