Download and read the "Getting Ready for the SAT Subject Tests" guide, which is available for free on the College Board's website. It will give you information about the format of the test, how to register for the test and the rules of the test. It also includes sample test questions and a list of tested topics, so you can familiarize yourself with the format of the questions and the content that will be on the exam.
Take a full-length practice test exam before you begin to study. Analyze the questions you got wrong. Separate the questions that you got wrong into sections based on historical time periods or events. Spend more time studying areas where you missed a lot of questions. For example, if you missed eight questions about World War II, but only four questions on World War I, you will want to spend twice as long studying World War II. You can obtain full-length practice tests from the College Board in their online store.
Create a realistic study plan for the amount of time you have before the test and stick to it. Do not cram for the test. Try to give yourself at least an hour per day for four to six weeks prior to the exam. Study each day, but make sure to give yourself time to relax as well.
Gather the materials you need to study. Helpful materials will include notes from your history classes, a general world history textbook, and test preparation books. Test preparation books are very helpful, as most contain an outline of the content you will need to know, quizzes, and full-length practice tests.
Take one full-length practice test per week. Block off one hour for practice tests, the same amount of time you will have on the actual exam. When you take your practice test, do so in a quiet place under test-like conditions. This will help you get a better idea of how well you will do on your actual test. If you are not scoring as high as you would like to, adjust your study schedule to include an extra hour of studying each day.