Applicant's relationship to author:
- author's identification (position, title, etc.)
- author's relationship to the applicant (employer, professor, etc.)
- length of time author has known the applicant
- frequency of interaction
intellectual capacity of the applicant:
- attitude toward coursework
- curiosity
- learned skills with respect to course
- performance consistency
- contribution to class/work/position/etc.
- analytical skill
Personal characters:
- interpersonal skills
- organization
- emotional stability
- fill in the rest on your own accord here
Also, ask the person who is writing if he/she belives that he/she could write a strong LOR for you. Be honest and sincere and let them know that this is very important to you. It's your future!
If you have four letters, each letter should address separate aspects of you as a person and/or your application to medical school. The goal is to convey to medical school, through all four letters, the whole image of you as an individual, the one that they want to be in their classes!
Hope this little guide helps! Good luck!