Being a good traveler is simple: Blend in and be prepared. Though you can't change your skin color or the languages you speak, both of which are becoming less of a problem, you can take some easy steps to make your travels better. By better, I mean having a more authentic experience and make memories that recall culture and scenery as opposed to buffoonery and stress.
Blending in is hard for a traveler. You often have packed pockets, wrinkled clothes, running shoes and map. What you need is to look classy and prepared. Replace the maps, travel guides and fanny pack for things that anyone would have. Download those maps and guides onto your smartphone or kindle. Lighten your load and wear clothing that looks at home anywhere. A nice shirt with sleeves you can roll up and some slacks that are packable and wrinkle free are essential. Wear shoes that are casual but walk well in. Make that investment because, Like Forest Gump says, "You can tell a lot about a person by their shoes..." Those simple things will make less of a target of you and allow you to look on instead of being looked upon.
Lose the backpack, the photography bag or the huge travel tote. Grab a the new Bagpack. It something that looks at home anywhere on anyone. This might be the one item that changed travel for me more than anything else. It allows me to grab things in a flash as a messenger bag and wear it all as a backpack if I'm walking a long way. You'll have to fight your way through some local bias if you talk people with a worn backpack or huge camera bag.
Lastly, go with some words and a plan. When I travel unexpectedly the hardest thing to do is to have a productive agenda. Luckily, there's always someone who's been there before me who has done way more research than I have ever had time for. Find that guide and make it your own. Take a look at where that is going to take you and substitute what you want where appropriate. Deviating slightly here and there usually provides the most succinct way to get what you want out of your travels and still be efficient.
Always know the currency and basic greetings. Know how the currency is relative to your own so you always stay in budget. Also, know a tad about the culture, specifically if it is or isn't frowned upon to bargain. In most situations, a little haggling is expected but is some places it will make people angry. Some words and phrases to always know: Numbers 1-10, hello, goodbye, thank you, you're welcome, bathroom, left, right, how much, good, bad, near, far, dangerous, safe, bus, train, plane, time, hotel, police, help, hospital, food, sleep, time, happy, sad and when.
Lastly, grab pair of good sunglasses to hide those tired and vulnerable eyes and you're good to go. Travel is easy when you take less and know a little more. Take a look at my SMEDS blog to optimize your gear to be prepared for anything.