Before you teach in China - research
If you want to teach in China, finding a job is relatively easy - it's finding out if it's a decent job that's tricky.
The largest and best-established repository of information for those who teach here is at eslcafe.com. Unfortunately the list is not very well arranged and messages are deleted after a time rather than being archived. You will also notice that the vast majority of posts are negative - don't worry about this unduly. Bear in mind that people who teach in China and have a bad experience are much more likely to leave messages than those who go home contented and smiling. It's also worth remembering that there are no vetting procedures for posting on here - any social misfit with a drinking problem can come along and complain about what could have been a perfectly reasonable school which objected to their teaching while drunk.
A Google search is essential - not just on the name of the school, but the city and the province too. You might find a reference to the school on an obscure message board or homepage, or be able to get in touch with someone who used to teach in China and heard reports about the school you're interested in.
Before you come, ask the school to put you in touch with former teachers, and be somewhat suspicious if they claim to be unable to do so - either they're a new school, and you are likely to run into teething problems as they cope with their first foreign teacher, or their previous teachers have nothing good to say about them.
One essential resource for anyone coming to teach are the mailing lists run by Teflchina.org. There are three lists, focussing on jobs, life and teaching. These lists are archived and searchable, and if you don't find what you're looking for, subscribe and ask a question.
A list of 'mentors' - those who used to teach in China and are willing to be contacted about schools they've worked at previously - is also maintained by Teflchina.org. Don't be put off by the annoying pop-up dialogue box and cheesy fade-in effects, it's not going to break your computer.
Finally, travel discussion boards such as the Lonely Planet's Thorntree are often frequented by people who taught or teach around China and a question here might yield results.
If you do manage to find information, and it's all negative, what should you do? This happened to me a couple of years ago - a post on eslcafe.com lead to an email exchange with a guy who 18 months after leaving the school was still happy to write expletive-splattered emails denouncing the school and everyone connected with it. I looked at the information from the school and the information from him, decided I trusted the school more than I trusted anyone who would bear such a bitter grudge for so long, and accepted the job. It turned out this was the right decision. However, at that point I already had a years experience in China and some Chinese language under my belt, so I was prepared to walk away from the job if necessary - something that would be a lot harder for a new arrival.
If you don't find any information at all - do you like adventures?