1. Your "Strong interest" in the school, even saying "I'll withdraw from all other medical schools if accepted to xxx" if you mean it
2. THings you like about the school, in terms of curriculum, teaching mission/philosophics, strength in certain research/clinical areas, location, etc.
3. Updates about your grades, awards, publications, activities (Include only those that will be significant. If you get a 2.0 GPA for this school year, I wouldn't include it unless the school asks you to )