The Advanced Placement Tests (AP tests) are generally considered the most prestigious set of standardized tests available in the United States. Each AP test is supposed to be taken after a one year long course of study, following an official AP curriculum published by the Collegeboard, and using one of a particular group of textbooks. The highest scores on the AP test – it is scored from 1, the lowest, to 5,the highest – will usually be sufficient to earn a student credit in college, and failing in that, at the very least to allow the student to place out of an introductory course.
The AP program has two history courses, the AP World History course, and the AP United States History course (also known as APUSH). While there is some measure of overlap, it is unwise to take one course and assume that you are prepared for both tests. The overlap is slight, and it should be noted that it is easier to go from AP World History to AP United States History then the other way around. This is because the World History course covers three thousand years of human history, across six continents, and that timespan and geographic reach include the entirety of APUSH (although APUSH goes into far more depth).
The first step to taking an AP test is, of course, to take the corresponding course. While it is possible to self-teach an AP class, this is substantially easier in “idea-based” subjects, like Physics or Math, where any forgotten fact can be derived on the spot. The World History course is “fact-based,” meaning that if you are only 80% prepared, you cannot derive your way through the missing 20%.
The next step is to buy an AP practice book for world history. Your local bookstore, be it Barnes & Noble, Borders, or some smaller retailer, should have these in stock. I personally recommend Barron’s or the Princeton Review. Buy the book about a month before the test, and devote about an hour every afternoon for that month to reading each and every chapter of the book, and doing the associated practice questions. Also go on the Collegeboard’s website, and find the Document-Based Questions for the last few years. The DBQ will be about 40% of your AP test score, so practicing those will be a great help. About one week before the test date, start doing the practice tests in the back of your practice book, though you should focus more on the multiple choice section on these than you should on the DBQ.
On test day, get some sleep and bring something to much on during the break. Good luck!