Given my first hand experience with a seat on a Board of Medical School Admissions, I can tell you that medical school letters of recommendation can play an important role in swaying an acceptance one way or another. Here's my advice on how to ensure your medical school letters of recommendation represent you in the best possible light:
Request the letters sooner rather than later. You don’t want your recommender to write a hurried or less than thoughtful letter - give them time to reflect. Many students also underestimate the length of time it will take the recommender to complete the letter, and get it to where it needs to be. Asking recommenders well in advance of your target submission date will go a long way in preventing any delays of your application.
Visit, write, or phone your letter writer. Bring them up-to-date on what you’ve been up to, and provide them with an updated CV. It will give them more (and fresher) topics to work with. If it is a professor you had in a large class, the fact that you got an A won’t be enough to impress medical schools. You want the professor to have as much information about you as possible so they can write a specific recommendation.
Choose a recommender with whom you have a close relationship - but not too close. You want your recommender to have confidence in you - and what he/she writes about you. However, choosing a close family friend may not be the best idea, as this person will be less than objective - plus the letter reader will know this and take their recommendation with a grain of salt.
Ask for a letter that will focus on what makes you a qualified candidate. You need your medical school letters of recommendation to include your unique attributes and how those attributes will enable you to make a positive contribution to a medical school. The letter should be an evaluation as much as a statement of recommendation - it should provide the admissions committee with sufficient evidence and information to help in making its decision. It’s O.K. for your recommender to list what they like about you and your qualities, but ask them to emphasize why they believe you would be suitable for medical school.
Ask recommenders from different aspects of your life.All of your medical school letters of recommendation will be looked at as a whole, and the information gathered from them will be synthesized. Your recommenders should be a mix of people who can talk about different qualities that you have. A professor you had, a doctor you shadowed, an employer you worked for, and someone you volunteered with, will all be able to talk about you in different environments. 3-5 letters should be enough for schools to get a complete image of you as a person.
Mention of work habits is crucial. Medical schools need to know that you can handle the workload. Some applicants may believe that their time as a waiter or camp counselor aren’t relevant to their application, however activities such as these can show you are a hard worker, and can handle working with difficult people, two of the most important qualities for a medical student.
Ask your recommender to be specific - generalities fall short of explaining why you would be a good choice for medical school.
Ask your recommenders to visit the AAMC website.They should read the “Guidelines for Writing a Letter of Evaluation for a Medical School Applicant” and “Core Competencies for Entering Medical Students” which can be found here.