Be open minded, and be slow to take offense. Also, go with the flow. I went to India, and once I sort of just succumbed to the pace, I was really happy. Sure, I had no idea when my plane would take off, but it did eventually, and I was on it, so all was well.
Also, if you are in a poorer country, don't take offense that you pay more than the locals. Sure, that cab ride cost you 100 rupees when the locals get it for 60, but you are arguing over a quarter. And that quarter is a heck of a lot more valuable to them than it is to you.
(That's not to say to not bargain - but recognize that you may end up paying more, and that's okay.)
Find out what "friendly" means in the country you are going to. I found that my lack of eye contact, dislike of being touched, and shy smiles were actually seen positively in India. People seemed to respond to me better than to the typical American friendliness.
Plus, if you appear to be trying, and are open minded, people will forgive your mistakes. And I found in India, they love talking about themselves, and hearing about you - I learned so much, it was amazing.