Do not overtake on the right. If the police catch you, you will get into trouble.
Check to see how much life you have left in your tyres as you'll take a few mm off if you hammer it around.
Check your brake pads and discs to see if you have any slight warp. If you do get them changed before you go there as it will just get worse.
Filming is prohibited around the track and if you are unlucky enough to have an accident and they see filming or timing gear in your car you will get into more trouble.
The ring is in the rural RheinlandPfalz area of Germany, where the majority of people do not speak good English and some will refuse to speak to you in English so some basic German would not go astray.
Unless your car is built for hammering it constantly, it is a wise idea to do a lap or three and then come off for 5-10minutes to let everything cool down. The ring is much longer than most other tracks and the elevation change is ~300m, so it hammers every part of the car.
Some people do get sick on the ring, so some of those band things might be necessary.
Hope that helps.