If you really want to, get one of the comprehensive MCAT prep books from Kaplan or TPR or whoever and follow along in the sections as you cover them in your classes--they'll highlight the important points and what concepts you need to remember.
If your reading comprehension skills are lacking, I don't think it's ever really too early to start practicing verbal. Even if you don't want to do passages, start reading the editorial page in the paper every day and read articles in magazines like the Atlantic Monthly, Economist, Harper's Weekly, etc.
If you're doing well in your classes and have enough free time to worry about the MCAT, get involved with a club, or research, or hospital volunteering. Or maybe go out to a party or something every now and then, it's good for you.
edit: wow, i used a lot of ifs