I think the best thing you could do is take one practice test per week. The same day you take your practice tests, review all the questions you got from that test. That way they're still fresh in your memory. I would recommend Manhattan GMAT practice exams.

In between tests, go over what you feel are your weaknesses.

With this strategy, you can get in a good 3-4 practice tests. Combining the practice exams, with the problems from the OG 12th edition, should give you an good source of practice problems.

Finally, for your last practice exam, do the one of the tests provided to you when you signed up for the GMAT. I found that this particular test was very similar to the actual exam and I think your score on the real exam will be close to the mba.com practice test.

Also, Manhattan GMAT has a great source to study for the essay portion of the GMAT. I didn't look at any essay stuff until the day before. I wrote two different essays the day before just to get a feel for what it would be like. On the actual test I got a 6 on the essays. These really aren't that difficult don't stress too much over them.

Good luck.