Jeffort is right. Buy as many preptests as you can. The more practice you get for this exam, the better. Since it tests you on certain logical principles, your recognition and familiarity with those principles is key. The more you see of them, and the more questions you answer about them, the higher your score will be. Moreover, taking actual past exams gives you significant insight into how the test-makers write questions. There are several question types in each section. Recognizing those question types helps you understand what the test-makers are looking for in terms of an answer.