I really don't think that should be your focus during summer freshman year. If you really want to do something to benefit your likelihood of getting into med school, I would advice you to volunteer, do leadership, research, earn $$ etc...
For the MCAT, you could probably start studying summer of sophomore year and you would still be way ahead of the curve (If you're planning to take it as a junior/end of summer). If you do really want to study, I would start ochem. That way you'll get better at gen chem and do better in your classes as well.