A few years ago, I had a GRE student who diligently worked through all five of the Manhattan Prep math books in its GRE series. For those of you who don't know, that's a lot of math.
Wow! She's going to do really well! I thought.
Looking back, I realized the main problem was that by the time she finished all of the books, she had forgotten most of what she'd learned, since too much time had passed since she'd seen certain concepts.
Regardless of how intelligent a student is, there's a learning principle that makes a lot of sense to me:
Study something when you're starting to forget it.
If you study it when you still know it, there's little point: the memory is still there. If you study it too late, the memory may have atrophied to the point that it's effectively gone.
By studying something as you're beginning to forget it, you can rebuild the memory to make it stronger the second time. Kind of like a muscle after lifting weights: it rebuilds and becomes stronger each time.
Now, combine this principle with another one: that you should be increasing the amount of time between reviews of the same material. For example, study a word today, then two days later, then four days after that, then eight days after that. This tends to work because each time, you're strengthening the memory, so it will take longer to forget. This makes studying more efficient; you're not reviewing everything all the time.
Here's a tool that will help: timestamp the math concepts and questions you study so you know when you did them last. This will help you keep track of when to review.
If you're not sure when you're forgetting something, err on the side of caution and study it earlier than you think you need to. But strive to keep increasing (perhaps doubling) the amount of time between successive study sessions of the same material.
This process not only needs to be done with math concepts, but also with ETS math questions. If you got an ETS math question wrong, you need to redo it, but then you need to redo it from scratch when you're starting to forget it. Of course, those of you who have talked to me know the other things you have to learn from ETS questions: optimal method, concepts tested, reasoning opportunities, etc.
Like most things, when you need to review may well be different than when someone else does. But make sure you build review time into your study plan, so things really become embedded in your memory by the time you're done.
Studying for the GRE is harder than many people make it out to be, huh? Anyone who tells you GRE prep is easy is trying to sell you something. :)