Some basic points:
Avoid paying large sums up front - just dont do it.
Draw up a short list, ring them up, go visit, talk to current students ideally away from the management, get a warts and all picture. Look at the fleet, more important than the type of aircraft, is the serviceability of the fleet. Is there a single point of failure ie just one multi engine aircraft. Have they got a sim, does it match the aircraft etc etc.
Most problems with cpl/ir training is an aircraft going off line, and training grinding to a halt.
Lastly a good school can turn bad very quickly - just by an aircraft going off line or a key staff member leaving. So take note of recommendations from friends etc, but bear in mind that situations change overnight. With that in mind dont commit to anything too far in advance. Best get groundschool out of the way, before you spend to much time looking at schools for the flight training element.