Here is a list (in brief) of things you shouldn’t do on your adventures (abroad or otherwise). They’re guaranteed to make your travel experience better for everyone involved, you included.
Travel Don’t #1–Strutting around half-dressed. If you wouldn’t pump gas in your speedos at home, don’t do it somewhere else, just because you’re on vacation. Also, being fully-dressed, at all times in public, unless on the beach, is a great idea and will win you points with the locals and perhaps make you some friends, no matter how awesome your six pack is.
Travel Don’t #2—Assuming you can say whatever you want because locals don’t speak “your” language. If you speak English or Spanish (my two main languages) chances are a large chunk of people almost anywhere you travel will understand at least some of what you’re saying. Keep your rude comments under your breath or to yourself, at least until you get back to home sweet hotel.
Travel Don’t #3—Don’t behave badly because you assume you’ll never be back. Examples: don’t undertip–service people that provide good service deserve their just reward; don’t drink too much (alcohol) and puke all over public property, and if you do, clean it up; don’t break the law because you see locals doing it too, or hop on public transport with no ticket. You are making a bad name for tourists and travelers everywhere, and probably notably for tourists hailing from your country or region. Negative stereotypes about all sorts of people are built and reinforced by jerks on vacation that can’t be bothered to behave like normal human beings. Don’t be part of the problem. Be human and treat other people you encounter on your travels as such.