Studying Without a Plan - Some test-takers take a “more is more” approach to GMAT prep. That is, they take practice test after practice test, and think that will be enough to improve their score. Doing this, you run the risk of simply repeating the same mistakes over and over without any tangible improvement.
Not Using Computerized Adaptive Practice Tests - It’s important to mimic the conditions of the GMAT when you study. Prep books can be tempting as they advertise themselves as “comprehensive” study guides (and they can certainly be helpful in providing overviews of each section and test-taking strategies)
Not Focusing On Your Weaknesses - Some students focus on all sections and question types equally or spend more time on the sections in which they’re already excelling and want to boost their score by a few extra points.
Cramming - It can be tempting to try to shove all of your GMAT prep into the last few weeks before the exam, but whatever you do, don’t try to cram! Studying for the GMAT takes time, a prep routine, and a plan.
Not Getting Enough Rest - Pay attention to your emotional and physical health as you prep for and go into the exam, in addition to your mental preparation. The week before the GMAT, you should still be prepping
Refusing to Guess - Some students have a tendency to agonize over GMAT questions they’re struggling with or to take too long on the first five to 10 questions. The GMAT is not designed for you to get every single question right.
Not Taking Notes - Sometimes, test-takers make the mistake of not taking notes on the provided scratch pad as they read a question or figure out the answer. This might seem like it will save time, but not taking notes might actually lead you to take longer.
Rushing Through Questions - Many test-takers mistakenly try to save time by rushing through questions and answer choices without fully reading them. You need to read the passage and each GMAT question fully to 1) keep track of all the information you’re being given, including any significant details, and 2) know what the question is asking you to do.
Trying to Beat the Computerized Adaptive Format - Some students try to guess the difficulty level of a given question as they go along or otherwise try to “beat” the CAT format of the GMAT by focusing more on hard questions than on easy ones.
Calculating Data Sufficiency Problems - Data sufficiency problems ask you to determine whether given statements or pieces of information are sufficient to answer a mathematical question.