Improving quant, I agree with my two colleagues, does involve strategy, however, I think we can go a little deeper than this.

1. Identify in all your work what kinds of questions are you getting wrong. Data Sufficiency benefits more about 'thinking out of the box' as compared to straight 'problem solving.' We believe the GMAT is a great indicator or 'snapshot' of you as a business person. As such, a way of thinking that includes standardization and efficiency, as well as calculated risk, is how one should approach the test.

2. Memorize equations and relationships (such as quadratic equations, exponent rules, group formula, statistics, etc.) This will buy you time and accuracy.

3. While 'Plugging In/Backsolving' works somewhat, it really is a technique best used on algebra and DS. It is most useful on the SAT and GRE, rather than the GMAT, where you need to leverage math skills more. So make sure you're fully flexed.

4. Our clients use a state-of-the-art adaptive online program which gives students homework (untimed), quizzes and CAT drills (timed) (about 5000 questions) which gives them an accurate reading of what you're getting wrong, and how your timing compares to the average test taker's timing.

The material also demonstrates a 360-degree exploration of how math works, ie. how absolute value works in every situation, instead of the most obvious way, which is how many books review it. Using a program like this, is an air tight way to gain mastery over the math as well as timing. Which is why all our clients use it.

And about VERBAL:

I would actually challenge you about improving your verbal score. We've work with folks like you all the time - - its about targeted, clear changes, a result of looking over your mistakes to understand WHY you continue to get certain questions right and others wrong. Then make the adaptations and changes.

Good Luck!