Things you can do to lessen your "touristiness"

Learn a few key phrases. No one expects you to speak the local language, but it's helpful to learn basics like "hello," "thank you," "please," and "where's the bathroom?" It also endears you to most natives (save the French, who generally--and stereotypically-- aren't charmed when you butcher their mother tongue). Many of the wonderful invitations and experiences I've had came from my willingness to respect the local culture, no matter how idiotic I sounded at the time. Even pointing to sentences in a phrasebook is more polite than Speaking.English.Loudly.and.Slowly. to someone who obviously doesn't understand you. I never head to a non-English-speaking country without a Lonely Planet Phrasebook.

Learn a bit about your destination. You don't need to memorize the entire history of, say, Portugal, but it's helpful to read up on the country, its people, and customs. It will help you to understand certain quirks, the cuisine, religious practices, etc. It also helps prevent you from committing irritating, inadvertently offensive acts like insistently speaking Spanish to a Portuguese bus driver (I'm talking to you, Mr. Clueless Backpacker on the Faro-to-Seville route). That's a relatively innocuous crime, but things like touching a person on the head or pointing your foot at them (Thailand and other parts of Southeast Asia), making the "OK" symbol (Brazil), or exposing bare shoulders if you're a female visiting a mosque are decidedly not cool, and can have unpleasant repercussions. Don't be that person. Behave Yourself: The Essential Guide to International Etiquette is a great--and funny--crash course on global customs.

Use your indoor voice. As Americans, we're known for our friendliness, enthusiasm, and eagerness to express our opinions. Not bad traits. But in a foreign country, these things, combined with our notoriously high decibel level, can be misconstrued or just plain obnoxious. Along the same lines, curb the American tendency to boast, and know when to let certain comments or behaviors slide--sometimes, you need to bite your lip, and remember that you're the visitor. It's never worth compromising your personal safety (or that of another) to voice an opinion, but by all means, do stand up for yourself if you're at risk.

Dress appropriately. This generally applies more to women than men, but in general, why would you want to draw unwanted attention to yourself? Leave the frat shirts, booty shorts, and low-cut tank tops at home. While this is a basic personal safety issue, it's also about cultural respect. It's tacky and offensive for a Western woman to sunbathe topless in Southern Thailand (which has a sizeable Muslim population), but it can be seriously problematic for her to show too much skin or not wear a headscarf in certain rural areas of the Middle East.

Lend a hand. While some might see this as uber-touristy (if not outright patronizing), I often bring useful items with me to certain countries. Whether it's colored pencils or clothing for kids, basic medical necessities, or fresh produce, the fact is, isolated and impoverished people are often grateful for assistance. I won't bring or distribute items without doing a bit of research to see if it's acceptable/what communities are in need of.

Eat as the locals do, or at least pretend. For me, street food and dining in a private home are the greatest joys of travel. But not everyone feels that way, and sometimes, even I find myself confronted by a glass or plate of something so repulsive/high-risk, I can't bring myself to partake. To refuse an offering can often cause disgrace or mortal offense to your host, so if at all possible, fake it. That banana chicha, fermented by a heaping dose of my (likely tubercular) host's saliva? Yeah, I didn't really drink that.

Wear your poker face. I've often been told I have an expressive face (usually not as a compliment). When I'm traveling abroad, I have to work overtime to not show emotions when confronted with a cultural foible or other situation that amuses or offends my American sensibilities. And while losing your temper can occasionally work in your favor, remember that in many parts of the world--most notably, Asia--it's seen as a major character flaw. Take a deep breath, simmer down, and please don't unleash the "But I'm an American!" card.

Rules to follow as a tourist

Be humble and gracious. You may find the local diet, standard of living, and treatment of women appalling, but you needn't need show it.

Be respectful. You're the foreigner speaking a crazy language.

Don't be a victim. Use common sense, and don't go looking for trouble. If it finds you anyway, try resolve the situation in a non-confrontational way, or do what you need to do to protect yourself. In a worst case scenario, call your nearest embassy or consulate.

Be prepared. Always have a Plan B, whether it's money, copies of your passport and medical insurance, or taking out travel insurance. Email yourself and family or a friend copies of all important documents, including lists of emergency contacts, doctors, and collect numbers for banks and credit card companies.

Be grateful. No matter what kind of amazing adventures I have, and no matter how much my nationality/government/deeply ingrained personal and cultural shortcomings may embarrass me, I'm profoundly appreciative that being an American grants me the quality of life and civil liberties I possess.

[Photo credits: NY, Flickr user Baptiste Pons; Las Vegas, Flickr user geoperdis; Mona Lisa, Flickr user Gregory Bastien]