Looking through practice exams, OG problems you have already done, etc., do you notice any patterns in the types of problems that you miss (take longer to complete)?

In terms of resources for improving, I liked practicing through the PS and DS sections of Kaplan 800. I also did every quant question in the OG 11 and the OG-Green Quant book. I tried to hold my average to 1:30 per question every time I did an OG set (didn't always do that, but attempted to). By trying to hold a faster pace on these OG practice problems, I think I increased my speed for the exam. Read the explanations in the back of the book after you do a set of problems. Make sure you understand how to do every question. Even if you answered a question correctly, still review it. You may be able to figure out how to do it quicker. Also, Don't be afraid to re-review the math of whatever prep book you used in the beginning or the math review section in the OG books.

GMAT Prep questions were as close to the real thing as I got during my prep. Review those after you take a practice exam.

I agree that working out of the OG is the best way to go. Make sure that you spend time analyzing every problem - don't just do the problem and move on. After trying the problem (give yourself a couple minutes), look at the answer, and spend a significant amount of time trying to find alternate ways to do the problem, asking yourself why the incorrect answer choices were put there (are they traps?), maybe even changing the numbers/situation in the question to see what would happen.

It is through that sort of analysis that real improvement comes.

Good luck!