For a majority of candidates, scoring beyond 49 in the Quantitative Ability section and beyond 39 in Verbal Ability section of GMAT is a difficult task. In fact, the combination of QA – 49 and VA – 39 will get you a GMAT score of 720. So begin by looking at how far away you are from these sectional scores. If you already have a score of, say, 48, in Quant, then working very hard on Quant will not improve your overall GMAT score much - at most by 20 points. The improvement will have to come from the Verbal section in this case. And vice-versa if you have a Verbal score of 37 or more.
Do not assume that an unsatisfactory GMAT score means that concepts are weak. Your concepts may be excellent, yet you may not score well. The cause of the poor score could be Test Taking Strategy. Do you have a well thought out Test Taking Strategy in place? How good is your time management throughout each section? Are you selective in answering questions? Can you maintain your concentration level throughout the test, or does fatigue get the better of you? These factors are equally important. Don’t focus just on concepts.
If you solved 2000 GMAT practice questions last time and scored 640, you may have concluded that to get a GMAT score of 700 or more, you will have to practice at least 5000 questions this time round. And also get hold of as many tests as possible from all sources. But before you try this, it is necessary to understand a simple truth about GMAT preparation, namely: The Quality of your practice is ALWAYS more important than the Quantity of your practice.
The more material you seek, the more poor quality material you are likely to refer to. Remember, there is limited availability of high-quality practice questions for GMAT, especially for the Verbal section. So don’t take chances with just anything that has a label ‘GMAT’ attached to it and is ‘Free’!
Clearly, the plan you followed the last time you took GMAT has not given you the desired results. If you choose to follow the same method of GMAT Prep, albeit more intensely, you are unlikely to achieve your objective of a higher GMAT score. Before starting out again, get back to the drawing board. Perform specific micro-level detailed analysis of your strengths and weaknesses. e.g. within sentence correction: parallelism errors/idiom errors/modifier errors etc.. see which ones are you able to pick up and in what circumstances? Then find realistic, well-reasoned solutions to the areas that need attention. There are no shortcuts. Discipline yourself to diligently follow the steps you have now outlined.
In most cases, a gap of about 6-8 weeks between two attempts is sufficient. Do not stretch this much further. Remember, as you allow more time to pass by, you are that much more likely to utilize the time inefficiently or lose the recency effect of the knowledge gained in the first attempt. If your score in the first attempt is 670 or more, then it is advisable to have a second attempt scheduled with within 5-7 weeks of the first attempt