Before even attempting the MCAT, you should know that it tests knowledge gained through the med school prerequisites, which are:
Chemistry
Organic Chemistry
Physics
Biology
and to a lesser extent, statistics and even English
Now, most people will tell you that the English part is kinda a test of English language and that it doesn't really matter.
They are right. The essay part is barely looked at. So as long as you can make coherent sentences, you should be OK.
The next thing to do is to figure out how well you take tests. Your SAT score should give you a hint, and actually, your SAT score will correlate with your MCAT score. Remember, both tests are APTITUDE tests, so they in essence test how well you take tests, or in other words, how smart you are, NOT how much you studied.
If you had to take review courses for the SAT or ACT, then I suggest taking another one for the MCAT. It will be the single most important exam of your life (though just one exam in a long line of exams if you are planning on medical school).
Kaplan has an excellent course, and Princeton Review is also great. Just remember: these courses aid you in taking a test. They will teach you strategy and the like. They will also teach you the core material, but in reality, you could take this test after high school alongside your SAT and get about the same score you would get in college.
Personally, I did NOT take a review course. I received a 1500 on my SAT (this is back in the day; 1600 was perfect) and on my MCAT I received a 36 (13 Physics, 12 Bio, 11 English). If you check, these scores roughly correlate with each other, so if you did very well on your SAT (without a review course) you should be fine on the MCAT without one.
On the other hand, if you barely scraped by on the SAT even with Princeton Review or the like, be prepared to work for your score on the MCAT, and even then, don't be disappointed if you don't score very high. Remember, it is an APTITUDE test. It tests how well you take tests, not how much you studied.
So, now you know the biggest secret: this test does not test knowledge as much as you expected. That means the rest if test taking strategy. So, other than taking the expected courses, how do you learn to take a test?
Practice, Practice, Practice!
The good thing about courses like Kaplan are that they not only provide you with a rough review of the material (if you need it), they also provide you with tons and tons of test questions. They can also simulate the actual exam. If you cannot afford Kaplan, any MCAT test book should be fine. It is important to go through as many questions as you can.
Additionally, you should take at least TWO test condition exams. One two months before the exam, and the other two weeks before the exam. This is mainly a stamina builder and preparation for the nerves that most people get before an exam. Kaplan or such can provide such conditions. For me, my college actually offered this for like fifty bucks. I think it was two test condition exams and one take home exam...either way, it was more questions.
The thing that has helped me most with taking exams is a lot of reading...I read anything. I even took a speed reading course in high school, so I read roughly 3-5 times faster than a normal person (and I don't mean skimming). If you are more than a year out from the MCAT, this is the best thing I can offer. Practice reading! Read anything! Find something you love to read, and read read read! The more you use it, the faster you'll get, and you won't even realize it.
That's another reason for tons of practice questions. You get used to reading them. They are always roughly in the same order, and test prep places always tell you to read the last sentence first, then skim the question, pulling out pertinent details. That is fine, but if you read fast like me, you can skim the entire question, focus on the last sentence, then READ the entire question again. This way, I never make the silly mistake of answering incorrectly because I misread the question.
Also, it is good to find out what type of test taker you are. Most people have time at the end of an exam to go over answers. Do you:
1. Change answers from correct to incorrect?
2. Change from incorrect to correct?
3. Change from incorrect to incorrect?
Everyone does all of these, but how many questions of each do you do? Good to find out while you are doing practice questions. If you have more #2 than #1, keep changing your answers. However, if it is the opposite, you should probably just turn in your test at the end without going over answers at all because you are liable to make your score worse.
Personally, if you have tons of #2 (incorrect to correct), you may want to see if you are rushing too much through an exam just to finish, only to realize you misread or misanswered a bunch of questions that had obvious answers. In that case, SLOW DOWN. There really is no need to finish a test early, unless you just want to leave early (that's me).
And finally, it's all about stamina. Keep it up. I only look at the clock after I get halfway through a section. I know I'm fast enough to finish, so why keep looking? More pressure? No thanks.
And if I see I question where I'm totally stumped? Pick C or D...honestly. Flip a coin, see if C "feels" better. Whatever. C or D. Statistically, they are the correct answer more often than not.
You can also mark the question to come back to at the end of the exam, which I sometimes do if it is a long calculation question, but if it is a deficiency in knowledge, usually no amount of time poring over the question and wracking my brain will bring up the right answer, so I don't even worry about it. I put in an answer.....strategy....
How about retaking the exam? Most people do about the same if they do the same things before the exam, so if you score low (or high) and are looking to get a better score, you will have to invest in more the second time around....
More time studying
More time practicing
More books
More courses like Princeton Review or Kaplan
And do not get discouraged. I know people who got into good schools with scores in the high twenties. It is mostly about the exam, but there are ways around a low score as well. You are aiming, however, for at LEAST 30!
Good luck!