Hi there,
You should be finished with your pre-med coursework by the end of your sophomore year. During your freshman and sophomore years, study for your course exams and master the material.
When you hit the Fall of your junior year, get a couple of MCAT Review books and start to review. Set a schedule on the weekends and spend 3 hours or so reviewing. Do a major review over the holiday between your first and second semester of your junior year then go back to your weekend schedule.
You should be more than prepared by April of your junior year. If you do not feel prepared by the time to register for the April exam (by scores on retired MCAT exams) then put the test off until August but realize that if you take the August exam, your AMCAS application will not be complete until October. If you are a student who needs to apply early, then taking the August exam will place you at a disadvantage.
Also realize that the MCAT will go to computer in 2007 which will open up other days which might not be as late as August. The bottom line: Take this test only ONE time and score well. Do whatever you have to do to get a good solid review. Nothing looks as bad as a string of mediocre MCAT scores even preceeding a good score. Take this test only once and be prepared.
Resist the urge to memorize for the MCAT but rather be able to apply the principles learned in your pre-med courses to the problems that are asked on the MCAT. Learn to be a good problem-solver and not just have a string of things in your head that you cannot apply. Most undergraduate institutions in this country train you to be good memorizers but you have to take the next step and learn to problem-solve and think critically.
Learning to problem-solve is done by practice so get plenty of practice. Retired MCAT exams are available from the MCAT registration site on-line.
Good luck!
njbmd