Learning some Thai language before you visit Thailand is recommended because it will give you more freedom and independence. Knowledge of spoken Thai will not guarantee that you get the best prices in the market, but it doesn't hurt to know how to ask. Most importantly you will be able to appreciate the Thai people more, and they will certainly appreciate you.
Basic words in Thai language
Hello (Man says) = Sa Was Dee Krup
Hello (woman says) = Sa Was Dee Ka
Thank you (man says) = Kob Khun Krap
Thank you (woman says) = Kob Khun Ka
How are you? = Khun sabai di mai?
I am fine thanks (man says) = Pom sabai di krap.
I am fine thanks (woman says) = Chan sabai di ka.
Basically women say "ka" at the end of a sentence while men say "krap"