As somebody applying to med school, I figure I can give you a few hints (actually it turned into a short essay):
FIRST YEAR
-Seeing that it's your first year, don't worry about extracurriculars. Focus on school. This is important because it will ingrain in you the type of study habits that will help you be successful over the next three years.
-With that said, if you feel like you got school under control (I would wait to at least see your first terms grades) it wouldn't be a bad idea to join a intramural sports team or some other the club for the sake of at least having it on your resume at this point. Try to aim for a club that focuses on community work. There's no need to invest a lot of time into these just yet as you still have 3 years ahead of you. Plus, clubs and such don't hold as much weight on your application as clinical experience and research.
-This summer try and find research position. If its "prestigious," then all the more power to you. However, I would suggest finding something that you're actually interested in. Research can be very boring at first (i.e. just reading and summarizing journal articles), so you don't want to lose interest right away. Don't get hung up in the prestige factor.
-The second thing you want to do during this summer is volunteer at a hospital where you can gain some clinical experience. You probably want to start volunteering as soon as summer begins so start looking for places and programs this winter break. A lot of times, colleges have volunteer programs at a nearby hospital where you can gain clinical experience in "rotations" (i.e. you might get placed in Labor and Delivery for 2 months, and then moved to ICU for the next to months, etc.). This is also a great opportunity to find a doctor to shadow. If you do end up shadowing for somebody this summer, make sure to keep in contact with them. These men/women can often provide you with a strong letter of rec.
-Put in a very solid amount of time on research and volunteering over the summer so you can ease on the gas pedal during your sophomore year. Keep up with both activities (especially research) but in a much more moderate amount. I personally didn't spend more than 10-12 hours a week on these during the school years.
SECOND YEAR
-Just as you did in the first year, focus on your studies. You'll probably be running into O. Chem and Physics and Biology classes now, so its important for you to do well in these classes. Not only do med schools look at them closely, these classes will also provide a good foundation for your upper division classes; that is, it'll help make things a bit easier later on (but not too much easier!). You might also want to devote a little extra time to the clubs. If there is a chance to get any position, take advantage of it (I would aim for the less time-consuming positions). It'll help your clubs stand out a little more. Once again, try to join stay active and play intramural sports (great stress relief and another thing for your app). Start looking for summer MCAT prep programs during winter break and sign up for one that starts around the beginning of summer (more on this later).
-Hopefully, by the end of your second year you have an idea of whether you want to enter med school right after college or want to take a year off. I personally took a year off and can't imagine not having done so. At the same time, going straight to med school will not set you a year behind and there's a smaller risk of losing your academic intensity.
-If you want to go straight into med school, take this summer after your second year to prepare for the MCAT's. By this time you're probably done with your lower division pre-req's and a lot of that material is what you see on the MCAT's. So it will only help that the material is fresh on your mind, rather than waiting till the summer after your junior year. Plus, this frees up your third summer so you can focus solely on med school applications (makes it much less stressful and I highly recommend doing this). Also, and hopefully this isn't the case, it gives you more time to retake the MCAT if you're not satisfied with your score. Take a course like Kaplan or Princeton Review over the summer. In addition, buy the Exam Krackers books (cannot emphasize this enough). Hopefully the course ends a couple weeks before your actual MCAT test date so it leaves you with extra time to take practice tests (get these for the official website).
-Maintain research and volunteer. Try to shadow again if you can. Doesn't have to be as intense as first summer since you are now preparing for the MCAT's as well.
THIRD YEAR
-The mantra remains the same: focus on school work. Your MCATs should be out of the way so really try to excel in school this year. These will be the last full year's amount of grades that will be on your transcript before the application period starts. Do you best to absolutely kill it this year.
-Spend a little more time on research and volunteering during the school year.
-Start zoning in on the people you want to be writing your letters of rec. Get 2 science professors, 2 other professors, 1 from the volunteer program, 1 from research (should be the primary investigator), and maybe from the doctor you've been shadowing. Let them know by February or March of your junior year so that you're not stressed out later on. Also, try to sit down with these people and let them know what areas you want each person to emphasize in the letters.
-Starting end of April or early May start looking at the AMCAS application on-line and start filling it out. You can't submit it till early June but this way you'll have it ready by that time. The primary app is not too bad. Just asks for grades, extracurriculars, and a personal statement (get help on this if you feel you need it). Create an Excel spreadsheet where you can mark off that all the schools have been sent what they ask for.
-Volunteer and research during the summer.
FOURTH YEAR
- Do well in classes, return all the secondaries you get (can be a little time consuming), and schedule interviews. Schedule these as at the soonest available spots.
-Once you get your acceptances keep your grades up but enjoy your life for the next few months. You deserve it. Hit up Vegas or something so it gives you something to look forward to.
Let me know if you get any more questions. I'm currently getting back interviews so I can help you up to this point. Sorry for the length (just think of it as practice for the MCAT verbal section).