Here's my two cents to add to UMP's:
You need a different strategy for improving for each section. I have improved the most in PS with my studying, so I'll focus on that.
Physical sciences is about knowing the formulas and concepts well, and of course, not making careless calculation mistakes. I would say content review is most important in physical sciences for most people (that is to say, most people taking the MCAT have a major somehow related to biology, if you have a physics or engineering major, then I think BS will be most "high-yield" for you).
Another thing about physical sciences is that you should realize that a lot of different concepts can often be related (similarities between kq1q2/r2 and Gm1m2/r2 is often cited as an example, as well as similarities between fluid flow and electric flow, but there's a lot more.. S.H.M. has to do with waves, and waves can be generated by an oscillating electric field, which creates a force on an elastic string, or generates an EMF, or.. etc. etc. Light emitted by stars can also be represented as energy, and do work, or can be used to calculate the speed of the stars due to the Doppler effect etc. etc.).
This is directly out of EK's book but, "the key is to find the simple science concepts behind the difficult questions".
Verbal Reasoning I haven't really improved in.. so, I can't really give advice.

Like most people, I seem to lose 90% of my marks on 1 or 2 really hard or off-the-wall passages. I think it's true that it's the most difficult to improve in - I usually finish with 30 minutes left, but if I force myself to use most of the time, my score doesn't improve, in fact, I just spend more time getting stressed and second-guessing myself.
Biological Sciences, know your trivia (hormones, physiological systems,e tc.) and know how to interpret results. I wouldn't stress Orgo if you haven't gotten the Biology stuff down first. For example, when I got my first Hardy-Weinberg equilibrium question on a practice MCAT, I only remembered the p2 + 2pq + q2 = 1 formula. Suffice to say that didn't help very much (I ended up trying to solve a quadratic.. didn't go so well) without the crucial p + q = 1!
For BS I'm going to be making flashcards for all the facts I have to remember (definitely hormones, but other things too, like difference between osteoclasts & osteoblasts, steps in meiosis, etc.). However, like PS, it's also very interconnected; especially between nervous system & hormone system. Try to see the human body as a cohesive homeostatic system, I think that will help a lot.
Good luck.