And at the risk of being repetitive...
...don't pay up front, however much it looks like a good deal. Because 1) they may go bust, 2) you may decide flying isn't for you, 3) you may wish to change to another school for some reason - and you won't get your money back in any of these situations.
And don't think it can't happen to you - I'm currently training someone who lost several thousand pounds when his previous school went tits up.