Take an official American Government CLEP practice test. You can pay to download such a test from the College Board website or find a practice test in a CLEP study guide book. Take your test with only a paper and pencil in a room with no distractions. Time your test and don't go over the allotted time.
Score your test and review the answers. Make note of every answer you missed, paying extra attention to that topic when you are studying.
Study American government by reviewing an online study guide, taking an online course, or reading an American government college textbook. Focus on the structure and history of the Constitution, the branches and powers of the federal government, and the political process of elections. You do not need to study state or local government for this test. Take notes on everything you don't know and make flashcards of the facts you need to remember.
Practice your flashcards every day. If possible, use a friend or family member to quiz you.
Take another practice test when you are about two weeks away from taking the CLEP test. Assess how much you have learned. Spend extra time studying the topics you are still missing questions on.
Give yourself a 24-hour break before taking the CLEP test. Be well rested and eat breakfast in the morning. Bring your ID card and two sharpened pencils to the testing center. The CLEP test does not penalize for wrong answers, so answer every question.