Autobahn Rule 1: No passing on the right!
The first thing any driver needs to know about the rules of the autobahn is that passing on the right is verboten! It is illegal to pass a vehicle on the right. You must move into a left lane in order to pass. (The only exception is when traffic is moving at a very slow rate of speed, such as during a traffic jam.) The pass-on-the-left-only rule is one of the things that make the autobahn work.

Autobahn Rule 2: Double check your side-view mirror before moving into the left lane!
Always check your left side-view mirror! Especially on sections of the autobahn with no speed limit, this is critical. Speeding cars can suddenly appear out of nowhere and zoom past you at speeds exceeding 100 mph. You may be doing the “recommended” speed of 130 km/h (80 mph) and see German drivers passing you as if you were standing still.

Autobahn Rule 3: Slower traffic stays to the right!
As in the US, whenever possible, move into the right lane. Most German drivers are good about this, but some non-German drivers are not. If you are passing several vehicles in a row (usually trucks), you can stay left or in the middle lane, but as soon as there is space, move right. If you see a vehicle coming up from behind you at a higher rate of speed, signal and move over. Don’t be surprised if they flash their high beams. It’s common and only considered mildly rude. Just move over.