First of all, there are five exams released by ETS. What worked for me was doing the exams in test-like conditions (taking my time and even filling in the answer sheet). After each exam I did, I reviewed some concepts I missed, and then started another exam. I managed to do 4 of the practice exams - all except for the 2008 one. I got 990 in most of the practice exams, thanks to the curve, and 990 on the actual April GRE - which felt much easier. However, I think I tend to concentrate more when doing an actual exam, so your mileage might vary.