Luke and WHD,
You apply,you then get asked. After that survive 4+ weeks in standards probably without pay (minimum) relearning stuff some of which you probably never knew/taught (in the realworld). After that pass the acceptance rides, GH, multi, IR,Spin/Aero. 6 months or so probation and then your in. You may get in teaching the basic stuff and get upgraded later. Most of the schools have screwed down pay - leading to unhappy pilots. The big one pays its new guys the same now as they did 10 years ago. 0% inflation hey. Shop around, the market is fluid and a LOT of the established guys are leaving soon if the pay/bonus issues don't get sorted out. Generally if your good enough to get in then your good enough to go to jets/turbo's and a better career and longer term stability.
The really big outfits treat their instructors badly - you are just a small faceless cog. Talk to the guys at Oxford, Prestwick,Cranfield. Ive noticed they are always grumping about something over cofee. They can be found remoted to various small airfields as their main bases are bursting at the seams.
Its a lot better paid, the flying was fun when I did it but when the slump comes in 1/2/3 yrs......