AP Human Geography
AP Human Geography ranks among the easier tests you can choose to take. If you are planning on taking AP Human Geography and self-studying, there are a few classes I would suggest you take first. AP Comparative Politics covers a lot of the vocabulary used in Human Geography, so if you don't do any other prep work, I would at least have a firm backing in APCP. I would also suggest that you have knowledge of world/US/European history. It's always helpful to know about places and know who went there and why they did before you walk into the test only to be blind-sighted by names of places you have heard nothing about.
Otherwise, I would suggest that you purchase a review book. I used Princeton Review AP Human Geography, and it wasn't very in depth, but it had enough information to be able to figure questions out. The practice tests are not extremely realistic though. If you get around a hundred percent on the practice tests in the Princeton Review book, you still need to do a little more studying than you think. There are a lot of names of places on the test, so it would do you justice to just look at a map for a little bit and determine where exactly things are (even the tiny countries that you "don't need to learn").
Overall, the test isn't all too difficult as long as you can conjure up something to write on the free-response questions when you have no idea what is going on. I would suggest taking AP Human Geography as a self-study if you aren't up for a very big challenge.