I started with a practice test, just to figure out what the test is all about. I hardly studied for the biological sciences...I guess having a good record as a bio major really helped in that section.
I bought a book of practice Verbal tests which really proved helpful. It's so hard to keep interest in passages that are about the most boring subjects, but sitting there and actually practicing to develop focus and speed proved invaluable. I'd also suggest reading the newspaper as often as you can, and although it's torture, read through articles that you don't find interesting. Afterall, you can't weed out the uninteresting passages on the MCAT.
I had to flat out study for Physical sciences. There's a list of formulas/equations that are important for the MCAT...it's out there somewhere, I frankly don't even know where I got it. I started out learning the equations and their relevance, and then I reviewed the major concepts in a Kaplan review book.
Throughout the whole process, it was all about the practice tests. Take as many as you can, in as realistic conditions as you can.