Jet 2 seems to be doing well, so why?
First, its base airport. No loco competition for miles around. A massive local population, and these days there's money in Leeds.
Two, sticking to sensible routes and not trying to go head-to-head with EZY or FR, who would retaliate.
Three, obviously run by professional business people with experience of running an airline.
Four, cheap aircraft, owned not leased, in enough quantity to make expensive sub-chartering unnecessary.
Five, following the low-cost model without trying to invent something different that may or may not work (like Now's pricing, Debonair's frequent flyer programme, Buzz's choice of aircraft)
Pity I didn't think of it a couple of years ago......