Certain cultural differences are so important that, while they will be discussed in any good Thailand guidebook, they bear emphasis here.

• Do smile. Often. Thais smile for all occasions: To say hello or thank you, to apologize, to make a request, to smooth over bad feelings. And even because they're happy.
• Do learn three phrases, as recommended on the language page.
• Do show respect for the king. This isn’t just a guideline; it’s the law. Rise when the national anthem is played (typically at 8 a.m. and 6 p.m. in many public places, and before public events.) Never insult or joke about the king or royal family. As you learn more about the present king, Bhumibol Adulyadej, you'll readily respect him; in more than a half-century on the throne, unlike so many other rulers, he has been a powerful and positive force toward improving the quality of life for the Thai people.
• Do dress modestly. Thais now understand that Americans may show up in shorts and tank tops in public, but would never do so themselves. Wearing long pants, and clean, neat clothes, will gain you an extra measure of respect.
• Don't wai unless you know what you're doing. The wai — the slight bow with fingertips touching in front of one's face or chest — is a greeting, and a way of showing respect or thanks. But it's more complicated than that. If you return a wai to someone of much lower social status, for example, you may feel you're striking a blow for equality; actually you're just embarrassing the person. Unless you've got an audience with the king, a westerner can just smile instead of doing a wai. If you've got an audience with the king, you need a more exhaustive website.
• Do show respect for religion, for the Buddha, and for monks. Don’t wear shorts or tank tops to a temple. It's considered improper for women to touch a monk. Don't arrange a comical pose of yourself with a Buddha; tourists have been arrested for such offenses.
• Do not touch anyone on the head, a spot which is considered sacred.
• Do not point your feet at anyone. (It’s easy to do so unthinkingly when you sit cross-legged in a chair, or sit on the floor.) Feet, located at the opposite end of the body from the head, have an opposite status. Don't use your feet for anything except walking, and keep those feet off the furniture. (If you're studying to become a Thai kick-boxer, you need a more exhaustive website.)
• Do speak quietly and gesture softly. Loud voices, calling attention to yourself, pointing at people or things, throwing things, and making big hand gestures, all seem graceless to the Thai sensibility. In the U.S., making a scene might get results. Here, it gets you avoided.
• Do not lose your cool. At times, everything will move more slowly than you think it should. To show irritation or frustration will only make things worse.
• Do watch for con games. Anything offered for free probably contains a hitch: A free cab ride will include stops at knick-knack or gem shops. Even when you pay for a ride, cabbies and tuk-tuk drivers may try to deliver you to a shop, from which they collect a commission, en route to your real destination. Any jeweler with a printing press can sell jewelry with a certificate of authenticity. Don’t be paranoid, but do be cautious.