You need to brush up your school level math like algebra, fractions, percentages, geometry and data analysis. Of course the questions would not be that easy, but you need to get your basics right.
If you’ve just begun your preparation, your first step should be to solve all the math exercises in the Barron’s. In this book, each math concept is given separately followed by a set of exercises based on that concept. This arrangement is very useful because it helps to test how well you can apply the concept you’ve just learnt and pinpoint your weak areas. If you’re a non-math test-taker, the Barron’s guide is the most important part of your preparation because it covers all the basic definitions related to number theory (prime numbers, whole numbers, etc.) But remember that all the necessary concepts are not covered here
Look for mathematical shortcuts. Math problems can be solved many different ways. Try to choose the fastest and easiest method to solve problems found in the GRE quantitative section. Sometimes rather than doing the sum, you should be able to just look at the answer choices and have an idea of what the answer possibly could be, and then confirm it. Use the process of elimination. Often, you don’t need to do any work when you can easily eliminate the wrong answers
Keep track of units given in GRE quantitative questions. Some questions may ask for an answer to be given in different units than were used in the problem. and last but not the least thing you need is a lot of practice, nothing more, nothing less.