Memorize words on the list of high-frequency GRE vocabulary words found in study guides and online. Add words you cannot easily define to your personal study list.
Make flash cards for difficult vocabulary words. Review a few cards daily, adding more flash cards as you grow comfortable with previous words. Take the flash cards with you on test day and review again before you are asked to store your personal belongings.
Read the GRE antonym questions and answers carefully. Several answers may seem correct at first glance. Choose the best answer.
Try to figure out an unfamiliar word by looking at its context or breaking it down into parts. Remembering a phrase you have heard the word used in may help jog your memory. And, if you can recognize a word's root, prefix or suffix, you can use that information to piece together a definition of the word.
Watch out for answer choices designed to trick you. Some answer choices may remind you in some way of the word shown in the antonym question. Double check and make sure you are selecting the antonym.
Answer sample GRE antonym questions and take practice tests to become familiar with antonym questions.