The first thing I found strange was Ka and Krap at the end of a phrase or used individually. Women use Ka and men use Krap. Basically, it just makes a sentence more polite. If used individually after a question, they both mean Yes. If you get Mai that's no.

The Thai people are just too polite to laugh at you if you make a language mistake but they may smile a lot. Just go for it and have a good time. In the north they speak Central Thai, Northern or a mix of both. 99% of the time the people you will talk to will speak Central Thai to you and that is what is in all the phrasebooks.

Don't worry if you are visiting hilltribes and don't understand anything. They speak a dielect that most Thai's don't understand either.

Hello (male speaker) sawatdee krup
Hello (female speaker) sawatdee kaa
How are you? sabai dee mai
Fine thanks sabai dee
Thank you kop koon
Never mind mai pen rai

I don't understand mai kao chai (Mai at the front is like NO=No understand)
Do you understand? kao chai mai

Where is the rest room? hong nam yoo tee nai (hong nam=bathroom)

What is this ? nee arai ( If you are asking you may not want to know)

Good luck chok dee

Numbers
Zero soon
One nueng
Two song
Three sam
Four see
Five haw
Six hok
Seven jet
Eight bad
Nine gao
Ten sip

Thai also has four different meanings for every word depending on the tone. There are four tones in Thai, raising, lowering, high and low. So you can get phrases like this.

Who sells chicken eggs? Krai kai kai kai

There are also a million ways to write Thai into English and all the phrase books are not created equal, some are just put together much better. I have a big collection including some dictionaries but the best two are:-

Lonely Planet's- Thai Phrasebook - ISBN 86442-658-58 About $7 USD

Practical Thai - ISBN 974-8362-27-2 About $6 USD at all Thai Duty Frees

Both these books are clear and concise and both have the phrase in English, spoken Thai and written Thai. If you are really lost on how to say something you can just show it to the person. They are also small enough to put in a large pocket and cover almost everything you may need.