I took the GRE Biology test this year and did much better than I was hoping for. My study plan was pretty simple:
Go to bookstore that had the Princeton Review GRE Biology Book.
Copy the vocab list in the back of the book for notecard making (warning: do not actually buy the book to do this).
Download a copy of Reece Campbell Biology.
Read entire copy of Reece Campbell Biology (over ~3 months). I took notes on the material I was least familiar with, and printed out some of the larger figures as a study reference, such as the diagrams for glycolysis and the citric acid cycle.
Take one or two practice exams (one is on the GRE website).
I actually had the Kaplan Review study guide as well, and I would not recommend it at all, or any "study guide" for that matter. Much of the material was not presented in an organized fashion, and I saw many glaring errors in it as well. Every biology textbook will also have a study guide in it, and at least that information has gone through a rigorous and transparent editing process. The only use I got from it was the practice test, which I would not have needed to use at all if I hadn't already taken the free test on the GRE website as a benchmark.
Just to emphasize my point, there was nothing in the test that wasn't covered in Reece Campbell, and maybe 2 chapters in Reece Campbell that weren't covered on the test. I got the impression that the test was written by someone who was using that book as a reference. Seriously. Get Reece Campbell.