Human Geo is the easiest test I've taken so far for a few reasons:
1) it's the shortest (around a 2-hour time limit, I believe?)
2) questions pretty straightforward
3) free-response questions were about basic concepts (Von Thunen's model and the growing importance of less-known languages on the Internet)
It was a fun class thanks to my teacher, but he didn't prepare us that well for the exam. I would definitely suggest all of the things people have said so far AND to practice real Free-Response Questions from the website. I know you can't really score them yourself, but at least try to get into the writing style they're asking for.