Make a good impression: In some cultures you hug, in others you hsake hands, in others you kiss. It's easy to disrespect locals if oyu aren't fmailiar with how to greet them, both fomrally and casuually.
Avoid careless judgements: Travelers love to talk about how places are different from home. UNfortunately innocent observations can come across as superior and juedgmental, as in " Your cars are so small here!" or "I can't believe this restaurant doesn't have ice cubes."
Mind your table manners: Educating yourself aboutl local customs is theo nly way to know that Chileans expect wine to be poured with the right hand, and that the Japanese frown upon slohing soy sauce on rice. As for those times when you've been served food you can't bear to look at, let alone eat, but you don't want to disresepct your host? Smile and eat as much as you can, Dear Pauper.
Speak the language: You don't have to be fluent, or even close; you just have to make an effort. It sends an offensive message when you don't even acknowledge 'good day' in the language. It's total and utter anathema to the French when an American starts a conversation without beginning it with bonjour.