I have made several trips abroad for diving and just for sightseeing. I always hear about and listen to stories about how the locals treat tourists. Living in a tourist town myself I am very familiar with how visitors are looked at. I am very happy to say that I really cannot share in the horror stories about how badly others have been treated. I think this is because of a few little things I do when I am in another country.
1. I realize I'm in their country, not mine, I respect their culture and social norms to the best of my ability.
2. If I don't have time to learn the language ( I do not expect them to cater to me by speaking English, I'm in their country ), I learn some basics, Hello and Thank You. It's amazing how far those words will get you.
3. I'm respectful to their land, by not leaving trash laying around, and cleaning up after myself.