Remember, this is written by an American, for Americans (mostly).
First, if ever dealing with German cops....don't say anything stupid or act stupid. German cops are typically very professional and only stop you because you probably did do something of a violation. The minute you start acting goofy with them.....they can take you down, and cart you off to the police station. So when you drink out on the town in Germany....and the cops come to ask questions....be friendly. Don't go and do something really stupid.
Second, drinking. It's easy to guzzle down three or four German beers, and then realize that you just aren't in great condition to drive. So if you have to drive....you sip through one good beer, and then quietly call it a night. If you are drunk and the cops stop you....that license is gone for an entire year, and the money involved isn't anything to joke about.
Third, autobahns have various speed limits. Sometimes, you might think you are on a unlimited stretch....then suddenly come up on a 100kph sign. So you continually have to pay attention and adjust for speeds.
Fourth, construction zones on the autobahn. When they shift you over to a smaller lane....it is truly a smaller lane. It's typically just wide enough for a car to go on a straight and narrow path. There's a reason why you should only be traveling at 50kph in a construction zone. Don't take risks.
Fifth, follow the winter weather reports. If they say there's a hint of bad weather, and you were planning something on the road that day....don't do it. Germany is famous for having several inches of snow to fall in a short period of time, and you really don't want to be stuck between point A and point B, with no real spot to adjust your travel situation.
Sixth, don't board a train or subway car....without a ticket. The fine is usually hefty and not worth all the hassle involved. They will get their money in the end.
Seventh, getting lost is always an issue if you are traveling around in areas of Germany that you aren't familiar with. If there was a reason for having a GPS.....this is probably one of them. It even becomes a bigger deal when you've got a street address in Frankfurt, and start encountering one-way streets. So invest in a GPS.
Eighth, if you live in a house which is heated by oil.....you really ought to pay attention to the amount in the tank each month. I've worked with people who never paid attention to their heating oil, and woke up in January to find no heat....because of a lack of heating oil. To get on the schedule for a delivery? You could be talking about seven days. You really don't want to sit around for a week in winter....waiting on such a delivery.
Ninth, Germans tend to be curious people at what you paid for things. Don't overplay your hand and admit vast expenditures. It just ends up giving you a status that you probably would prefer not to have. When it comes to cars, vacations, and furniture.....everything relates to a status and the amount of money you paid.
Tenth and final.....American humor doesn't always work on Germans. So don't expect a laugh over some joke you heard from Leno or Letterman. It also works the other way....a German might tell a joke, and you have to pretend it's funny, but you really don't get it.