Generally speaking we Germans are friendly, welcoming people. There are a few things you should know before you come to Germany, so that your stay will be enjoyable and without awkward situations.
DON'T walk on the bike lane. Skip this tip if you are Dutch or have been to the Netherlands before, because then you wouldn't even dream of walking on the side of the street that is meant for bicycles. Germany has bicycle lanes in nearly every town and city and believe me, they are not only there for decoration. In both countries, cycling is very common and you can get run over from a cyclist because he will simply assume that the coast is clear.
DON'T do anything extremely noisy in your apartment after 10 pm. This means don't play loud music and above all don't start fixing stuff in your house with a drill, chain saw and so on. If you are from a western country you will think this is self explanatory, if you are from other parts of the world you will appreciate this tip :-) because your german neighbor WILL call the police. Okay, if he's nice he will knock on your door first to complain face to face.
DON'T come to a friends house uninvited. In some countries you can just stop by at your relatives house or your friends' whenever you feel like it. You wanna go visit someone spontaneously in Germany? Oh you better think twice. We value it if someone gives us a quick call or text message in advance . And somehow my grandmothers generation managed to inform someone from their visit, so nowadays its more expected than ever.
NEVER come to an appointment late, regardless of wether its for business or casual, just don't do it. Unless you want to be the unpunctual foreigner and feed the stereotype that "you guys" are always late, do yourself a favor and be punctual.
DONT' use someones first name in an official context. In Germany we have different ways of approaching friends and our authorities. You can have friendly chats with your boss at a barbecue and still call her Frau Dr. Professor Schröder, whereas in the States or somewhere else your friendly boss would tell you to call her Jane. Say "Du" instead of "Sie " to the wrong person and you will earn deathly silence, because its a taboo in Germany.
Thanks for showing interest in our culture and enjoy your stay in Germany.