Flying schools are quite highly regulated by the CAA, so you're likely to find that standards are fairly consistent, so far as basic maintenance and instruction are concerned.
So, what issues are worth looking at?
Price - important to everybody, but if you've just graduated particularly so.
Fleet - what sort of thing do you want to fly? Have they got more than one? Are you looking to build experience in the same place? if so, you want to see a selection of other things to fly once you're qualified.
People - can you reasonably guarantee to fly mostly with one instructor whilst you're learning?
Feel - an intangible, but go and do a trial lesson at a place, chat to the instructors and students, do you feel comfortable in that environment?
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