First of all, make sure that at some point you take some official mocks, which can be found in the GMAT Prep software and in the PowerPrep software that is a predecessor to GMAT Prep. Those are pretty close to the real thing. Otherwise, rather than preparing for the GMAT, in a way you are preparing for a test prep company's version of the GMAT, which may be close to the actual GMAT, and yet not quite the same.
So get GMAT Prep and PowerPrep. Yes, your score on a PowerPrep CAT can be inflated if questions that you already have seen in the Official guide show up on the CAT. Still, it's pretty useful.
Beyond that, you would probably be better off spending more time working on questions put into categories, and much of this on an untimed or at least lightly timed basis. That way you could work on strategies for each particular question type until you get that type down. I have worked on one type for two days until I felt pretty confident in that area. Then I worked on another type for a day or two. This tends to work better than just doing random questions, because this way you can focus on learning certain things and get a clear picture of how a certain type works.