I've been advising a lot of clients lately regarding letters of recommendation both for medical school and residency. Remember that your letters have a big impact on your application, and a mediocre letter can bomb your candidacy. Always ask your potential letter writers if they will write you a "strong letter" of recommendation. If they say no, hesitate or tell you they are too busy think of their negative responses as a favor.
For help with application strategy please contact me. The earlier in the season the better.