Most of the online advice I have read says that taking practice test after practice test is not beneficial. While there is definitely merit to the argument, if you want to get a high score you need to get your brain used to functioning at a high level for the full 3 hours you are in the test. Which means you need to take A LOT of practice test. Its a marathon not a sprint.
The argument against taking too many practice tests is that you are not learning anything new when you take the practice tests, and you need to do some serious review of critical information before taking another practice test. While this is true, I think the key last step to studying is training your brain to be high functioning for the full 3 hours. Once you know you are capable of getting your goal score, you then need to ensure that you can get it under less than ideal circumstances.
What I did was study just the GMAT material I needed by going over a full set of books and only took a practice test once a month for about 4 months. In the final weeks before my test I took a full practice test (including AWA and IR) every day, then gave my brain a break to rejuvenate and did no GMAT studying the two days before my actual test. It worked well for me, I got a 770 with an 8 on IR and a 5.5 on the AWA. (not to brag, but I kinda have to if I want you guys to take me seriously).