The Quantitative section of the GAT tests mostly math concepts that you all learned in high school or college, so your GAT preparation for math may boil down to simply refreshing those rules and formulas. Of course, if you did not do well in high school and college math classes, preparation for GAT Quantitative section can be a real challenge. Make sure you learn all the relevant formulas, especially those relating to topics you don't like very much. (Usually, the reason you don't like a topic is that you don't understand it.) For example, if you hate to see coordinate geometry, review those formulas with special care. Do not simply hope that you won't get any questions about a subject you don't like; learn all the relevant theory, and make that subject an essential part of your math GAT prep process.
The Verbal section, on the other hand, tests the theory that is not necessarily included in high school or college programs. It may be new to you unless you majored in English or took a logic class. For most native English speakers, preparation for GAT Verbal section does not require as much effort as math preparation, but you should make sure you are aware of grammar and logic rules; formal English grammar (the kind tested on the GAT) can be quite different from the kind of English you use in your daily life. For non-native English speakers, verbal GAT preparation can be a real challenge, requiring lots of time and energy. Make sure you know the grammar rules tested in Sentence Correction questions and that you can understand complex Reading Comprehension passages.
Practice
The second part of your GAT preparation is practice. Try to answer as many GAT practice questions as you can to get familiar with all the GAT question types and the tricks and traps that appear in GAT questions. The more you practice, the more you will get used to GAT questions and the less time you will need to answer them. Time your GAT practice sessions whenever possible, since you should get used to answering questions under time pressure. It's best if you use online practice tests so that you get used to answering questions on the computer screen, as you will on the GAT.
Analysis
The last but not least important step in your GAT preparation is analysis. Make sure you take some time to review all your practice tests, paying close attention to explanations of the questions you got wrong. Analyze your mistakes and review all the relevant theory to avoid repeating those mistakes.
For the Verbal section, try to understand not only why the correct answer is correct but also why wrong answer choices are wrong. This will help you learn to eliminate answer choices and will increase your guessing odds even when you are not sure what the correct answer is.
For the Quantitative section, read explanations even for the questions you answered correctly, in case there is a faster or easier approach that will help you save time on similar questions in the future.
Overall, GAT prep is not difficult, and if you organize it correctly, your score will improve significantly. Self-guided preparation is possible, but we recommend that you use GAT Online on this site or thecatonline.com, which contains all the theory, practice, and analysis tools you will need for your GAT preparation. However, you choose to prepare, make sure you have all the theory you need and sufficient practice.