The questions are not in order of difficulty. The OG is a great book, but it's basically a compilation of old tests with the numbers changed. So for every group of 20 or so, you'll get easy, medium, and hard problems.
BUT
The 10th edition was released with new questions that are, by and large, harder than the 9th edition. In the MC section, those are all the questions after 252 (you'll see a page break there) and in the DS, they're all after 155. Not sure about the verbal side, but I assume this is true.
To answer what you need to do other than that in the time you have depends on your level and how much you already know. If you've got it all down, but just need to practice, then just do the OG. If not, and you've got to learn all these concepts, then you should get some books. I recommend the Kaplan math and verbal workout books, although the math one neglects many of the higher level concepts, it does a great job on the concepts it does teach, and it has several hundred questions that are in order of easiest to hardest.
Other than that, just keep checking the board here - there are some great discussions going on to keep you in the game!
Finally, I have a free 2 minute lesson on my website that will definately be relevant to one of the questions on the GMAT. It always comes up once. Click below and you'll see it on the home page.
Good luck!