Being proud to be an American means more than most people would imagine. Freedom of speech, having the right to vote and having a Democracy are a few reasons Americans are proud. When you travel abroad to another country, your actions and behaviors reflect your country as a whole.
It's common for misconceptions of ridiculous behavior to be associated with Americans, such as underage over drinking, ignorant of other cultures and an ethnocentric belief that their country is the best. Letting stereotypes keep you from traveling and interacting with those who hold these misjudgments means missing out on the opportunity to represent Americans.
Learn a few words in another language: Just because you failed College Spanish doesn't mean you have to force yourself to learn the language if you don't want to for an upcoming trip to Mexico. Even if locals may speak English, it's common courtesy to at least learn a few words; such as “Hello”, “Excuse me.” and “Goodbye.” Especially when you're in a country where the native tongue is difficult, the effort is appreciated.
Familiarize yourself with local laws: Using the excuse that you're a tourist can only take you so far. This doesn't mean to recite every written word of their Constitution, but to know right from wrong. For instance, did you know that chewing gum is banned in Singapore? This is due to people disposing of gum incorrectly. Going against local laws can mean great danger in other countries; even if you are protected by your own.
Understand how business' work: Sometimes, Americans are spoiled and they don't even know it, especially when it comes to shopping. Our huge shopping complexes are everywhere and have longer hours that people are accustomed to. Don't be shocked if local stores close at 6pm or if you're in Spain and between 2-4pm and stores are closing for a siesta.
When in Rome, act as the Romans: Diving into culture is the best way to amplify the travel experience. Just because there is a McDonalds in Rome doesn't mean you should find yourself having lunch there every day. Trying local foods and local activities means breaking out of your comfort zone sometimes. Any local will find this admirable and you'll be able to understand the culture a little better.
Don't complain, be understanding: It's easy to find yourself frustrated during your travels when things don't go according to plan. But, complaining about things not being like they are at home, such as not being able to understand the language or finding yourself lost every day is poor character. Even if you don't like the local food or enjoy the city you're visiting, being respectful is the best way to keep foreigners from calling you a “typical American.” Even being honest in a respectful way about not liking something, but trying it anyway is also common courtesy for a traveler.