Are there any rules I should follow to be respectful around Germans?

Shake hands to say hello. Germans are great hand-shakers, and they like to do so both when arriving and departing. It is common for a person who is joining a group to shake hands with every single individual.

Be mindful of others when it comes to alcohol. Beer and wine are part of a normal dinner and alcoholic drinks are usually offered to guests. Not drinking, however, is completely accepted. Do not insist on alcoholic drinks if a person has rejected your initial offer and don’t order them for them. A German who rejects a drink is not just being shy or polite but does not want to drink. 

Don’t turn up late for an appointment or when meeting people. Germans are extremely punctual, and even a few minutes’ delay can offend. Be five to 10 minutes early for important appointments and be sure to call the people you are meeting if you really cannot make it in time.

Go green. Germans are extremely environmentally conscious and separate their garbage to facilitate recycling. If other people spot you throwing recyclable glass or paper into the regular garbage, they definiely won’t approve.

Don’t call people at home after 10 p.m. unless you’ve asked them first if it’s all right. Don’t expect to reach anyone in the office after 5 p.m. Monday through Thursday and after 4 p.m. on Fridays.

Prapere to share tables with strangers. It is common to share tables with perfect strangers when restaurants are full and very busy. Before you do so, however, always point to the free seat and ask, "Ist dieser Platz noch frei?" (Is this seat free?). Also, wish the other diners at the table "Guten Appetit." But don’t expect any further conversation at the table. It may be very welcome, but you shouldn’t force it. When you leave, be sure to bid farewell to your table companions.

Try not to mention the war. That whole area is still a sensitive topic, even though many of the people directly involved in the war have already died and young Germans and Austrians (reasonably) don’t really feel as much connection to or responsibility for the actions of the previous generations. Because of that, it’s not generally a topic that Germans will bring up in normal conversation, but they also don’t necessarily try to avoid it. It is undeniably part of their history that they acknowledge, but it would be smart of you to not be the one to bring it up when talking to Germans.