Closely aligned to this formality is the obligation to use the "Sie" form of address with people you don't know that well. This holds true for both work and social situations. Most Germans still feel somewhat uncomfortable using or being addressed by "Du" with those they are only casually acquainted with.
Luckily, most Germans under the age of 60 have loosened up on this considerably in recent years, but it's always safest to wait until your German colleague or acquaintance (especially if they are older than you) suggests that the two of you can switch over to the "Du" basis. These days, it can happen within weeks rather than months or years, as was often the case in the past.
After you have developed friendly relationships with people here, you may find yourself invited to their homes. This should be a pleasant experience: Germans like hosting others and the rules of etiquette are rather uncomplicated. For instance, it is always advisable to bring along a small gift when invited to someone's home. Flowers, a bottle of wine, or some small souvenir from your homeland are considered most appropriate. (But don't bring roses; many Germans still associate this with romantic intentions and such a gift can cause a bout of confusion.) Also, do inform your hosts beforehand if there are certain foods (especially pork) or drinks that you cannot have.
Germans, as a rule, tend to be very fond of pork and are not always aware of the dietary restrictions others have. Plus, alcoholic beverages are a key part of most dinner parties here. They are happy to adjust the menu for guests, but let them know beforehand to avoid embarrassment at the table.
Another subtle difference that can cause uneasiness, especially when you're invited to someone's home, is the matter of the toilet door. In complete contrast to many other societies, Germans prefer keeping that door closed when not in use.
Leaving it open can be very offensive to some Germans. So how do you know whether that little room is occupied? (And in Germany, it usually is not the bathroom, but a separate little room.) You knock, preferably softly.