Make a point of learning a couple of key phrases in the local languages: Please, thank you, do you speak English, the food is delicious - these are good ones to start with.
Smile and be friendly. You'd be surprised at how many foreigners forget to smile and be friendly.
No matter what you'll do you'll stand out as a tourist, and that's not necessarily a bad thing. Trying to fit in would ironically make you look even more foreign, so I wouldn't worry too much about it. Making the effort to be friendlier and to speak a bit of their language usually helps a lot.
Oh, and Americans are famous for talking very loud. You could try lowering your voice.
And go easy on the local booze. You lot are famous for not being able to hold your drink.
