I will start off with some common sense information like your drivers license. Of course if you are not a German citizen your drivers license probably does not authorize you to drive in Germany. You will need to contact your local license branch (BMV) and find out the steps you need to take to receive an international drivers license. I have not personally done this because I have a European military drivers license but from what I have heard it is not too hard to do or terribly costly.
Next of course is having a car to drive when you arrive in Germany. This is pretty obvious. Coordinate with any INTERNATIONAL car rental service and they can have a car ready and waiting for you at your arrival city. Another option is to rent the car in Germany, which is a pretty easy process as well. Most service representatives speak English and will be happy to help you out.
Now you will need to know the meat and potatoes of driving in Germany, the traffic laws. If you are an American, or have driven in the U.S., you will find that driving in Germany is not much different. Without telling you every single travel law written in Germany, I will try to shed some light on some of...