Due to the big tourism industry and students going to study abroad, English teachers are in great demand in Thailand. Teaching English is one of the few jobs Westerners living in the country can do in a legal way. As formerly teachers only had to be a native speakers, now a bachelor degree is required to teach.
There are openings in regular schools, elementary as well as high schools, language institutes, universities and Thai companies who look for teachers to teach English to their employees. To find out all that is available you only have to check all the different websites and decide what works best for you.