I did an engineering internship for 8 months over there. I had to take mandatory German lessons in the evening.
German people are wonderful. They are cold on the outside but just as warm and friendly as any Canadian once you get to know them.
Do not declare a religion otherwise you will have to pay a Church tax (Kirchensteuer) which is given to the religious authorities of your congregation. (You can get a waver although it is easier to just claim you are not religious). Whatever you do, DO NOT LET YOURSELF BE DRAGGED INTO A RELIGIOUS DISCUSSION. Most German couple don't get married despite religion and politics being inseparable.
Stores are closed on Sunday.
Use last names, not first names for people you work with and specially your superior as it is a sign of familiarity and can be seen as disrespectful. Using first names is reserved for friends and family. Use "Sie" instead of "du" when addressing people who are not close to you.
"Freund" (Friend) is reserved for true friends, not just anyone. Unlike English, Germans don't like you calling them "Friend", "Buddy", "Dude" or by any other word that implies familiarity. When referring to someone you don't (or barely) know, the proper word is Bekannter (acquaintance).
If your food comes in a plate, always use a knife and fork to eat, never your hands. German people use the fork in their left hand and knife into the right hand and they don't switch the fork from hand to hand as we do here.
Try to eat everything that's on your plate even if you are full, otherwise the cook will be insulted and you won't get re-invited. <--- this is important!
If you walk into a room and the door was closed when you arrived, close the door immediately after entering or when leaving. Always knock on a closed door first before entering.
Don't be shocked if you rent and apartment and find no closet or no kitchen appliances. It's normal over there.
Expect dogs in restaurants and don't expect ice in your drinks because ice cold drinks are viewed as unhealthy.
NEVER EVER tap your forehead with your index finger, it is the equivalent to flipping the bird at someone and if seen by a cop, you could get a fine or get fired by your boss. Don't flip the bird either (they watch American movies too).
Don't change your mind all the time because this is seen as incompetence. If you must change your mind, make them present valid arguments, ask questions, don't give in immediately but conclude that you were convinced by their arguments.
Never EVER lose your cool or scream in public. Temper tantrums are seen as mental instability and are unacceptable behaviors, specially at work.
If you use a public bathroom and there is a lady there (men's room included), you are expected to tip the lady.
You can't generally add tip on your credit card, always have cash to tip a waitress or waiter. Credit cards are not accepted everywhere, even is restaurants.
If you are sitting alone at a table with empty chairs, be ready to welcome other people at your table if the restaurant is busy. They will do this without asking you.
Expect 16 yo kids in bars where they serve beer. Beware of girls who may look 18 but are really 16...
Don't swear in a Pub as it is considered poor manners and also there can be kids there. Children are allowed to be in a pub while with an adult.
If you order a Budweiser, you will be served a Czech Budweiser.
having a beer at work during lunch is sometimes acceptable. Having more than one beer at lunch at work is considered drunkenness.
When entering someone's home or apartment, take off your shoes and ask for slippers. Walking barefeet or in socks is considered bad manners.
If you rent a car, be careful to follow the speed limits, 50 km and in town 30 km. They have a ton of hidden speed cameras. If you intend to drive on the Autobahn where there are no speed limits, make sure you are capable of driving at high speed safely. Always beware of incoming cars that might be travelling at 260 km/h, never, ever block the left lane if you are not going at least 200.
Also be ready to brake in emergency as there are sometimes traffic jams, even on the Autobahn. If you can't see 1 km in front of you, don't drive faster than you know is safe. Trucks on the Autobahn rarely exceed 100 km/h.
German drivers are much better than North American drivers. Never try to do what they do.
Wow ! I think that pretty much covers it all... German people are reserved and do not go into emotional displays.
If you are unsure about how to act properly, at the table, at work, in public transit, just ask them, they will be happy that you are trying to learn their customs. If they show surprise at the cultural differences with Canada, I find that by saying that Canada is a huge country with a small population which forces us to act differently is good enough for them to understand we are not a bunch of barbarians.