AP Microeconomics is definitely harder than AP Macroeconomics. That being said, if you have already studied for Macro or if you have already taken the class for Macro, Micro will be a lot easier. The first unit for each class is essentially the same. You just learn about the basic laws of supply and demand and the basic laws of economics. Once you have these down, you delve into the specifics.
As far as Micro goes, you need to make sure that you know all of the key graphs and types of competition. This is probably the most important thing you will need to learn. Without that, you're pretty much a fish out of water on the free response section.
For preparation, I would suggest you use the Five Steps to a Five AP Economics book. It is pretty detailed as far as AP books go and it really helps with tips on how to draw the graphs (which is arguably the hardest thing to do, because the graphs are curvy). I would also suggest that you invest in the REA Crash Course to Microeconomics. There is a section in the back with all of the key graphs and formulas; even just reading over that right before the test can be a real lifesaver (it was for me).
Quick Tip: Make sure you know how to label your graphs! Even if your graph is wrong, if it is correctly labeled you will pick up at least one point!