Know your grammar and structure your lesson plans. As with teaching English to any non-native speakers, it is important to start with the basics. In order to teach the foundations of the English language, you may need to refresh your own memory regarding grammar, conjugation, and sentence structure. When drafting lesson plans, do not overload your students, but begin by teaching simple ideas one at a time.
Keep it exciting. Thai culture is based on the concept of "sanoook", or fun, and teachers who are seen as boring will have a hard time winning over their students. Using interactive games and activities to help students learn English will keep your students engaged.
Role play with your students. Using role plays and scripted and unscripted conversational activities with your students are useful and active ways to get them speaking and practicing English. Have them improvise conversations as they get to more advanced levels.
Smile. It may sound strange and contrary to your authoritative role to smile when teaching class, but in Thailand smiling is a very important to appearing polite and respectful. Showing anger or frustration is considered rude and can put you in a tense relationship with your students.
Be respectful of different cultural sensitivities. Two observations that many ex-patriot English teachers note is that it is important never to touch someone on the head and never to point your foot at something. In Thai culture, the head is revered and touching someone else's head or ruffling their hair is considered very rude. The feet, on the other hand, are the most reviled part of the body and pointing with them is considered disrespectful. As you learn such cultural idiosyncrasies, be respectful of them.
Help your students find ways to practice outside of the classroom. Thailand, compared to other Southeast Asian countries, has fewer opportunities for speaking and hearing English outside of the classroom. Setting up movie showings or having students meet for an English-speaking dinner party is a great way to incorporate English into their daily lives.