If you have some money saved then do some travelling around Thailand and see what cities you prefer. Lots of people start teaching in BKK and never consider other places. Lots of big modern cities all around the country with plenty of teaching jobs available.
If you can afford it spend July - September visiting places like Chiang Mai, Korat, Chonburi, Ubon Ratchathani, Khon Kaen, Surat Thani, etc. Hop on a bus and look around. Pick the one you like and start looking for a job in October. Don't rely on classified ads too much - better to hire a taxi and go from school to school.
If you don't like Thailand's other cities you can always go back to BKK in October and have no trouble landing a job.