Having been in Thailand twice this year and as a matter of fact having returned this afternoon, I would suggest that you not attempt to learn Thai before you leave. Tourist services usually have basic English; it is a required subject in Thai schools but the quality of the teaching varies incredibly.

I now know perhaps 7 words in Thai after two trips totalling over 3 weeks and have yet to have a major problem with a combination of English, sign language and a smile.

Price negotiation is done with a calculator. Many taxi drivers speak and understand very basic English. Most transactions with foreigners is done in English independent of the foreigners first language.

Since Thai is a tonal language, it is difficult for a foreigner to catch the subtilties of the inflection even if one knows the right word. Get a good map, be observant and friendly and you should do fine.