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!
"Having understood name-and-form, which is a product of prolificity,
And which is the root of all malady within and without,
He is released from bondage to the root of all maladies,
That Such-like-one is truly known as 'the one who has understood'." (Snp 3.6)
"Whether I were to preach in brief, Sāriputta, or whether I were to preach in detail, Sāriputta, or whether I were to preach both in brief or in detail, Sāriputta, rare are those who understand." (A I 333, Sāriputtasutta)