What should I be looking for in the instructor/school before committing...?
Without wanting to sound too flippant, basically the place that you are most likely to get work.
This will be determined by lots of things: do you already know the school involved (ie have you trained there already... remember your 'network')? How flexible are you? (ie are you willing to move? - there seems to be a few instructor jobs going in the NE at the moment - no good if you insist on living in London). What aircraft are you going to do the course on? (It would be a very brave guy/girl who didn't have the R22 on their Instructor's ticket?)
If you've got the time, go through the list that the CAA produces of all the FTOs and the courses they offer then go and visit all the schools offering the FIC. It would even be worth visiting the schools who don't offer an FIC to see where their instructors were trained. I'm sure that the same names will keep on coming up...
For the record, I did my course with Mike Green at Wycombe due to various recommendations. It was a great course (I managed to pass and got a job very soon elsewhere) but I personally wouldn't recommend Mike. PM me if you want further details.
Hope this helps,
B73
PS copter2424 - Not directly related to this thread but a small word of advice: Please don't offer to work for free. You're not doing any of us any favours...