1. Don't procrastinate.. it doesn't work in medical school.
2. Start the ground running
3. Get in a regular routine
4. Keep positive attitude
5. Realize this is what you want
6. When you get done studying, turn back to page one of your notes and start again.
I would tell myself to not compare myself to others so early on. I think I looked at a lot of students and heard about the types of students they were in undergrad and just assumed they were harder workers/smarter than I was. I would tell myself that med school is a clean slate and the past is pretty much nothing. I could tell the pre-MS1 me to not procrastinate, but I doubt it'd work.