This is not intended as a complete, definitive treatise on Thai pronunciation and phonetic spelling, but merely a guide to suggest the correct pronunciation and an explanation of the simple conventions I have chosen for spelling/pronunciation.
In fact, there is no standard convention for the transliteration of Thai to English. It is a matter of some debate among Southeast Asian scholars; if you ask five English-speaking Thai how to spell one of their words in English, they will offer five different versions and, probably, discuss it for hours. I theorize this lack of convention has to do with the fact that Thailand, contrary to some of its neighbors, has never been colonized by a Western power, unlike, for instance, Vietnam and Indonesia. Transliteration difficulties are further complicated by the obscure roots of contemporary Thai: predominantly Sanskrit, Pali and Chinese, with lesser etymological influences from its immediate neighbors, Ancient Cambodian, Laotian and Burmese. There are some Thai characters that have no approximate English sound; you must hear and imitate these to perfect them. Therefore, it is with some reluctance I offer my attempts at Romanization.