Learn some elementary Thai before you go. There are several courses on CD available. Many people there speak and understand English, but a few words in Thai (even with rather mediocre pronunciation) will be useful at the markets, and you will be praised as the greatest linguist of all times ...
It's fun, too. I learned a few rudimentary phrases from a Lonely Planet guide before going to Phuket and it's such a wonderful way to engage with the locals.
Phom chawp Thailand!
"Do not force others, including children, by any means whatsoever, to adopt your views, whether by authority, threat, money, propaganda, or even education." - Ven. Thich Nhat Hanh
"The uprooting of identity is seen by the noble ones as pleasurable; but this contradicts what the whole world sees." (Snp 3.12)
"To argue with a person who has renounced the use of reason is like administering medicine to the dead" - Thomas Paine