I hate that I think of my college years in terms of what I "regret" doing or not doing, however, you will thank yourself four years from now if:
1). You kick butt in the classroom. When you go to lecture, try and absorb everything the professors say. DO NOT fall asleep in class. It really isn't worth it. The more you absorb in class, the less you will have to study later. Make the most of your lecture time and studying time. Never get behind, so that you will have time to...
2) Enjoy yourself. College is the last time that you can act like a kid and really enjoy yourself. Work hard, play hard should be your philosophy.
3) Start studying for the MCAT 6-8 months in advance. Six to eight months is not much in the scope of four (or five) years of college. Yes, you will have to sacrifice a lot of time. But if you can get a 33+ (which is VERY doable, if u work hard), your application life will be SO much easier. And you DO NOT want to have to take that darn test a second time...trust me. I know very few people who did well enough the second time to actually have warranted the effort. Just go all-out for the first one.
4) Exercise! Most people's metabolism slows down upon entering college (thus the freshman 15, which eventually becomes the senior 25). If you work-out and exercise starting your freshman year, you can avoid that post-graduation gut.
5) Cherish your time. Life will never really be the same after you graduate. it's awesome that you are getting advice at this early stage.
Hope this helps.
Good Luck!