A few suggestions:
*One of the biggest things might seem too obvious to mention, but it's important enough to push on. You have to know your rules and strategies really well! It's not enough to *know how* to do something. You need to have the basics down so well that you can do the mechanical part of any problem with minimal effort. This frees up time and brain power for the little tricks and twists that are unique to each problem. Earlier in your education, it was important to know your arithmetic facts in order to perform basic operations such as division or solving an equation for x without taking forever or getting lost. Now you need to feel good about things like solving systems of equations, translating common word problem scenarios (rate, % change, etc.), and recognizing common patterns (quadratic templates, special triangles, etc.). You also need to be comfortable with the special question formats of the GMAT. (Many students take too long to develop a systematic approach to Data Sufficiency, for instance.)This kind of comfort often takes far more repetition and review than people realize.
*Do more up front. This is one of the most important things you can do to improve your score in both quant and verbal. In quant, this can mean several things. Have you clearly identified what the question is asking for? Have you simplified or rephrased the question? Have you actually written down an expression that you can fill in with the needed information? [e.g. Female Smokers/Total Employees = Female Smokers /(Male Employees + Female Employees) = ?] Do you clearly understand the difference between what the question is asking for and the information you've been given? (For instance, maybe the question asks for price per gram, and you've been given wholesale cost per 100 kilograms.) Can you estimate an answer? Can any of the answer choices be eliminated up front?
If you do this kind of up-front work, you are more likely to work through problems efficiently, because you will have a sense of purpose and direction pulling you through the problem. (And if you don't have that feeling, you may be quicker to recognize when a problem is too difficult and you need to move on. This is an essential part of GMAT strategy!)
*Redo problems. Ideally, you should redo every problem BEFORE checking your answers. After your timed experience, take time to work back through and look for other ways to approach the problem. What works best, and why? Is there anything you could have done to improve your speed or accuracy, even by a few seconds? If so, how could you have recognized that opportunity?
*Always stay open to new approaches. Don't keep doing the same things just because they are familiar, even if they lead you to the answer. Spend time looking at alternatives such as estimation, testing numbers, working backwards from the answer choices, etc. Even if you don't always *need* these tools very often, you will learn to spot opportunities if you push harder on these techniques more than you may strictly need to.
_________________