English can be political
Thai people are proud of the fact that their country has never been colonized by Europeans. However, the mighty tourist dollar and the ever-spreading Western pop culture can make nationalistic Thais worry that their culture is slowly being diluted. Private language school teachers may encounter students who want to learn English for job opportunities, but have disdain for the culture and people of the English-speaking world. Public school teachers may find that some of their students are purposely disengaged from language lessons. It's a touchy issue; one I feel completely unqualified to discuss in depth. But it helps to know that this mindset exists.
Never lose face - they won't let you!
The notion of "saving face" (maintaining an air of respectability) is capital-I important in Thai society, and this mindset applies to the classroom as well. Throughout my lessons, I would stop to ask the class, "does everybody understand? Are there any questions so far?" Every single time, the class would stay silent. Finally, a woman in a business English class told me discreetly that Thais would never ask for clarification, even if it was needed. It would be an implication that the lesson had not been taught effectively, and would cause the teacher to lose face. Rather than trying to break this habit in your class, you'd be better off finding more creative, indirect ways of posing this question.
You will often be mistaken for a tourist
For every earnest, hardworking, empathetic ESL teacher living in Thailand, there are hundreds of travelers and backpackers just passing through. Of course, many tourists are respectful of the country and its people, and truly interested in the culture. Unfortunately, the visitors who leave the biggest impression are the raucous drinkers, the ogling sex tourists, the naive drug mules, the fusspots who complain about the "weird spices" in their food. Thai people can be warm, hospitable, and charming, but they're also practical. They encounter flocks of Westerners with a very superficial interest in them. It only makes sense that some people won't have a great deal of initial interest towards you. Some effort goes a long way, whether you're learning the language, exploring the country, studying the history or bravely trying new local foods.
You will have to refine your sqeamishness
This isn't job-related, but living in Thailand means sharing your living quarters with ants, geckos, and (if you live in Bangkok), cockroaches. This is noteworthy because, in the initial culture shock phase when homesickness occurs, this might be a nail in the coffin if you're having a bad day. I'm notoriously shriek-prone when it comes to bugs and reptiles, but after a week or so it barely bothered me. Really.