i graduated med school in 1993.
first and foremost, i would have spent all five years of college taking Spanish courses. i can't stress to you enough how incredibly helpless you are when you can't communicate to patients. i had already taken 3 years of Spanish in high school and placed out of several college level Spanish courses, but that was nowhere near good enough to communicate complicated medical ideas.
a distant second would be to go into medical school with friends. because of my personality i tried to lone wolf it through med school. bad idea. you really need to have study partners. if for nothing else, you can vent steam with them. but you'll also find that there's no way to be on top of all classes at all times. and you're going to miss some classes due to illness and such. so it helps to have a study group. my suggestion is to locate pre-meds at your college and find out where they're going to apply. once you've all matched then become good friends with those going to your med school.
third, i'd prepare for clinical life. most med students find the first 2 years of academics rigorous but familiar. the second two years, in the hospital, are another animal entirely. i wasn't prepared to deal with patients and get my hands dirty. if you somehow get the opportunity it would really help you to be an EMT, or phlebotomist, or nurse, etc.
however, i'm sensing in your question that you are asking about academics. of course, you need to satisfy all of the med school prerequisites. but you really shouldn't let that stop you from taking the "recommended" courses. the ones i'd recommend are Biochemistry, Physiology, and Immunology. of those three, Biochemistry was undoubtedly the most critical.
another course that i sort of accidentally came upon and took was "Medical Terminology." it was offered in the Department of Classics and turned out to be the most relevant college class i ever took. knowing the Latin or Greek root of medical words helps you to know what they mean. so i didn't have to look up terms as often as other students.
lastly, i'm going to throw in a word for exercise. very early on in med school you'll start feeling the stress. that's when you'll notice your classmates hitting the gym. exercise, any kind of exercise, can be very beneficial to keep your mind clear. if you haven't developed any particular exercise regimen you should start hanging out at the gym now so you can find out what works for you. i lifted weights and played racquetball. others took aerobics classes. others yoga. some played baskeball or rugby. etc.
Best of luck!
I'm guessing you are asking more about academics in how you can prepare. However, I would suggest if you have any places you'd like to visit or any aspirations of travel, take the chance now while you can. Based on what I've seen from a family member going through med school, (who is now a family physician), you don't get a lot of free time. And any free time you do get, you spend studying and preparing for the next semester/exam/residency.