Take chemistry classes while pursuing your undergraduate degree. This means you'll have to do some planning ahead; but if you think you might one day need to take a GRE chemistry test, taking these courses and keeping your notes will definitely help you later on.
Study on your own. The GRE chemistry test covers four parts of chemistry: analytical chemistry (15 percent), inorganic chemistry (25 percent), organic chemistry (30 percent) and physical chemistry (30 percent). You can use books, such as Cracking the GRE in Chemistry, 3rd Edition, to help you study. Or, you can use old class notes.
Sign up for a GRE chemistry review class. Your local Princeton Review center might offer chemistry-specific review classes. You might also find professors at your college or university that will offer preparatory classes.
Practice GRE chemistry problems by trying sample tests. You can find some practice tests published by Educational Testing Services. These books will also offer you some information on the test format and scoring.