I spent over 4 years working in Thailand in various TEFL assignments. Below are a few pointers which worked for me when finding work.

Firstly before my arrival to Thailand the obvious choice was to fix myself up with a position before I left to take remove the pressure.
I managed to land my first job and have the interview in the u.k via an internet job search. The first thing that struck me was the lack of ease upon using these job sites. A particular new site I like is TEFLjobs.asia

Upon my arrival I had a place to stay, and all the important paperwork was processed.

What if I am already in the country?

I have also been down this route and for me it worked to get suited and armed with your C.V and original qualifications. If you’re in Bangkok then try the language centers. These work well and I landed a contract this way. There are companies you can use that employ teachers to be placed in local Thai schools. An added benefit of being recruited this way is most of these recruitment companies have contracts with local Thai companies. So you could be working for a school in the day and teaching business English to Honda Thailand in the evening.

Be persistent, don't give up. If you don’t have a reply from your C.V (photo must be included by the way) keep trying but you can’t go wrong by putting on your suit and being pro active.

First impressions are massive in Thailand so make sure you look the part.