Hi maray,
Since you have been studying for four months and scored around a 540 on your first practice exam, we should do some careful analysis of your study routine to determine why you have been unable to improve to a 700+ score. Remember, the GMAT is such a challenging exam because there are relatively few questions asked in a given exam, yet those questions come from a huge topic pool. Thus, the best way to get a great GMAT score is to have a thorough understanding of all the topics that may be tested on the exam. To develop such mastery, you want to strive for linear and targeted learning, and follow that with focused practice. In other words, you want to master one topic before you move to the next. Have you been able to study in this way?
For example, if you are learning about Number Properties, you should learn everything possible about that topic: LCM, GCF, units digit patterns, divisibility, remainders, etc. After that, be sure to practice with a lot of questions (50 or more) just on Number Properties. Doing such thorough practice will hone your ability to apply what you have learned to realistic GMAT practice questions. The more realistic practice problems you solve using proper strategies and techniques, the stronger and faster you’ll become at working with GMAT concepts. It is through this deliberate practice that you will continue to build sophisticated critical thinking, analytical reasoning, and decision-making skills, all skills that the GMAT rewards and that many students lack.
Follow a similar routine for verbal by learning one section at a time. When learning about Critical Reasoning, for example, you want to be able to learn about all aspects of Critical Reasoning: strengthen and weaken the conclusion, resolve the paradox, find the conclusion, must be true, etc. Follow up your learning with focused Critical Reasoning practice, so you can determine your specific weaknesses within that topic. You should do the same for Sentence Correction and Reading Comprehension.
If your current resources do not allow for such focused learning and deliberate practice, you might consider using a more robust resource, such as a self-study course.
Once you feel you have improved your GMAT quant and verbal knowledge, begin taking practice exams to track your overall progress. When taking practice exams, you may consider taking the exams offered by GMAC, since those exams have an accurate scoring algorithm and contain retired questions from past GMAT exams.
Please keep us updated with your prep and, if you have any further questions, feel free to reach out to me directly.
Good luck!