Im actually a pretty ordinary driver (at the best of times) and im too lazy to usually play much with the setup of the car.
I do know a fair few of the problems with cars though, as invariably i dont do much maintenance on the cars and they tend to need coaxing after a few months and im pretty fussy with things when i finally do get around to working on the car.
Personally if i could be bothered i would start with the setup of one of the team drivers and then play with the springs/shock positions/rear toe in depending on the class.