Get to know the common reasonings, practice, review and revise
Generally, to study for GMAT, you need to set a goal (your targeted band, time frame) and a detailed timetable. Depending on your current level and expected score, the average time to prepare for the test may vary, but I would say spend at least 4 months to 8 months to prepare for GMAT, since it takes time to fluent the skills needed for GMAT.
Start your GMAT preparation by the Official guide by GMAC – the creator of the test. The most updated book at the moment is 14th edition (2015). Read closely to understand the format of the test, test-taking suggestions, and the real GMAT questions – they are retired from past GMAT exams.
Also, install the GMATPrep software (downloadable at www.mba.com) on your computer. It gives you 2 full tests with detailed explanations, tips on GMAT, and many practice questions.
After taking the diagnostic test on Official Guide, start studying different parts of GMAT (Analytical Writing Assessment, Integrated Reasoning, Quantitative, Verbal) by different books on techniques to beat the test. Once you have finished the learning process, take the first GMAT mock exam on GMATPrep software. This will be a good representation of your current level since it’s a true GMAT test. If you are satisfied with the result now, take the second GMAT test on GMATPrep, then you are ready for your actual GMAT. If you want to raise your GMAT score, then I suggest buy some GMAT mock tests from Manhattan (you actually get 5 tests if you buy at least one of their books). Taking one mock test every 2 weeks, then carefully examine the answers, especially the wrong ones, to see the reasons and better avoid similar mistakes next time. Save the second test of GMATPrep before you take the actual GMAT. Again, this would be the closest representation of your current level.
Also note that as the test is computer-adaptive, i.e the difficulty level of the next question you’ll get depends on whether your previous answer is correct, the first 10 questions often play more role in deciding your level. If you answer the first questions wrong, it is really hard for you to recover to your initial level. So put more time on your first 10 questions to make sure you answer them correctly, then you might spend less time for the next 20 questions, even guess some if you are running short of time to ensure you get to the very last question. You will have to pay a heavy penalty if you do not finish the test.
Another experience of me is to focus on Sentence Correction (SC) – the seemingly easiest part of Verbal GMAT. Answering each SC question in approximately 1 minute will save you time for Reading Comprehension (RC) and Critical Reasoning (CR) – these two part requires more time to tackle. After I started focusing more on SC (by reviewing all SC in Official guide books twice), my SC success rate increased. Moreover, the more time spent on RC and CR also boost my performance in the two parts. After 2 months, my score on mock tests improved from 600 to 680 – 700.
For Analytical Writing Assessment (AWA), remember that the template is really important. Since the e-rater reads your essay by reading its structure, transitional words and key words, make sure you include them in your AWA. My advice would be to come up with your own template and start practicing 5 to 10 AWA essays (from the topic list on the Official guide book). That way, you can save time not to think about these transitional words and phrases, thus focus more on finding the flaws in reasoning and how to improve the argument.
For Integrated Reasoning (IR), the skills needed are those of Quantitative and Verbal parts, to do not worry too much about IR. Just save time to study the IR questions types, then do the IR questions in GMATPrep software twice, you will be fine.
Overall, the test is about preparation, so make sure you are familiar with the format of the test, what is expected, common ways of reasoning, and build up your confidence in taking GMAT. After all, GMAT is really beatable.