our sub conscious is actually pretty good at doing a lot of the work for you. Therefore visit the schools, spend some time there chatting to people and just getting a "general feel". Your senses will tune in to your new surroundings and you will build an opinion on the place. Don't rush it though.
Repeat this at quite a few schools and the combination of all your research will make your decision making a lot easier.
I know it all sounds a bit "hippy" but I found it worked. I walked into one school and immediately knew it was where I wanted to train. I of course stuck to my system of chatting to instructors, students and asking the important questions.
Oh and NEVER pay up front. I would say a small deposit is acceptable but if anyone is asking for more than that then thank them and walk away. It's tough out there and I'm sure there are a lot of places out there who above water look calm and relaxed but underwater are paddling like crazy to stay afloat.
One of the best bits of advise I've ever read on PPrune.
Also if you considering going to the USA - got there and visit to get a feel - I did and it was black to white the atmosphere at the schools across there and so obvious which were the better schools - but you wouldn't know that without visiting.