With regard to the GMAT, raw intellectual horsepower helps, but it is not everything. Manhattan Prep’s Stacey Koprince teaches you how to perform at your best on test day by using some common sense.
This time, I have got a short and sweet post for you. Take a look at your calendar, and find a weekend to take off from your studies (or even an entire week). Yes, I am serious! People tend to get really burned out studying for the GMAT; you will be doing your brain a favor if you give it a bit of a break. (Note in general: when your brain is fatigued, it cannot make solid new memories. Do not keep pushing yourself to study under those circumstances!)
Second, I have a few resources for you. I put together a couple of posts that highlight what I think are the most useful articles from recent years. Take a look at What Would Stacey Do? for resources and advice on areas with which you may be struggling.
I do want to take time to mention explicitly the one post that I think is the most important and the first thing that every GMAT student should read: What the GMAT Really Tests.
Third, recently we discussed how to study for Critical Reasoning. Here are two available resources:
Finally, go take a break! Take a look at your calendar, and find a good time to rest your brain. I have never met anyone who can study effectively for months straight without at least one solid weekend break (and an entire week is often better!).