I'm a complete hack at setups, but here's what I do...
Try setups from different "authors", either from Inferno or the old standby begging fast guys for their sets. Once you try 5 or 6, see what you like and use that for a base setup in that car for other tracks. Adjust final drive and left/right handedness (camber and tire pressure) and you're good to go!
Once you have a setup you like, you can tinker with things and see what happens.