MCAT Practice Test Advice

It doesn't really work like that. What you should do is the following:

1. Buy the AAMC online tests for $80 (unless your taking the April test, then just use the demo test for free)

2. Assess your performance and study in the areas where you performed poorly.

Unfortunately the MCAT is a standardized test, some people do well and some don't (and it doesn't necessarily depend on intelligence). You can change the range in which you have a tendancy to score, but it's very difficult.
The AAMC tests are the most accurate predictor of real performance, they are old MCATs. Plus AAMC isn't trying to scare you into paying $1500 to take a prep course.

AAMC online test site.

 

I don't think there's really a magic number of tests you should take. If you feel that you grasp the material well, do more practice tests. However, if you don't know the material very well, your time might be better spent trying to get a better understanding of material you are weak on. I would definitely second the above posters recommendation to buy the AAMC practice tests. I probably took about 15 practice tests (most of them I skipped the writing sections) and got a 30.