Really, this could apply to any expat, but here are some common things I've thought about since moving to a community that is half composed of Americans who live here as a result of the military. Some of these things apply especially to the military-affiliated people.
1. Stop being upset if a store/restaurant does not take credit cards and go with the assumption that they might not so carry cash instead.Yes, I was guilty of that too. Now I just always assume that I'll have to pay cash.
2. Please, please, stop asking if a restaurant is child-friendly if that means that one is looking for a restaurant that will be happy to accept one's children running around, screaming, standing on the tables, and not being properly monitored by the parents. All of these things have happened, sometimes with the parent not making a concerted effort to curb the child's behavior. This does not leave a good impression of Americans to our German hosts! It's not always possible to control every action of one's child, but in order to be respectful of the restaurant and other diners, parents should work with their children to learn proper restaurant manners. If the child is having a meltdown and it can't be resolved, it's time to take the child home and try another time. And, for the love of all that is good as well as for your children's development, please get a babysitter instead of taking your infant or young children to movies meant for adults.
3. Don't be afraid to leave the base if you are living there! So many wonderful treasures await outside the gates, ready for one to discover them. Especially in the Kaiserslautern area, it's not difficult to find someone who can help and speak English if one gets stuck. It's really not scary to go out there. Do a bit of research online if you are worried. Blogs, such as mine [shameless plug], are helpful for learning about how things work here.
4. Stop buying vegetables at the Commissary and being unhappy because they go bad quickly! I'm guilty of buying my vegetables at the Commissary too, but with the realization that I might be disappointed at the freshness, probably because there is not always heavy turnover. Go shopping on the economy; there are wonderful farmers' markets and Turkish markets often have some nice produce too.
5. Stop buying American gummy bears (if you do that type of thing), even if it's the same Haribo brand. Once you taste the German ones made with real fruit juice and no high fructose syrup, you'll never want to go back (trust me on that one).
6. Stop driving everywhere. If it's feasible, try taking the train or bus instead. You'll be thrilled at the ease and comfort of traveling as well as the relief of not having to drive in congested cities or pay for parking.
7. Don't expect Germans (or those of any different nationality, for that matter!) to be friendly in the same way that Americans are friendly. For example, being upset that people on the street don't smile or wave back doesn't do any good. Germans are known for deep friendships and authenticity but may take a while to warm up and get to know new acquaintances. Don't take this personally; instead, appreciate a true friendship if one develops!
8. Don't say things that you don't mean; it's inauthentic. Also, for people from another culture or who speak English as a second language, it is confusing for them (and it's not kind to anyone!). For example, expect that if you say "we should get together sometime," that the other person will be expecting that the "sometime" will actually occur, even if you didn't really mean it.
9. Stop being monolingual! At the very least, learn some common, polite German phrases such as hello, goodbye, thank you, please, etc. Become as fluent as what works for your situation. There are no and low-cost options out there to learn German. Or, even better yet, see if you can find a German-English tandem partner to practice. You may even make a German friend as a result!