That is a really, really difficult question. Plus, in my opinion, pretty irrelevant to learning to tune in the game. It is almost better to set aside real world tuning knowledge and learn what works in-game. Move a lever (setting) one way, what does it do. Move the same lever (setting) the other way, what does it do.
The reason that I say your question is very difficult is that you are about to receive multiple differing opinions and long descriptions about real world tuning, none of which have been proven to exist in the game. Good luck sorting through all of the advice that you are about to receive.
With that said, I will make an effort to answer your question. Understand that this is purely my opinion.
1. Camber is broken. Zero is fastest. Zero would never provide the fastest corner speed in any condition I race in the real world.
2. Ride height is backward. High front/low rear turns better than low front/high rear.
3. LSD has a very large affect on the car's ability to turn. My real world LSD cannot over ride my spring/damper settings.
4. Springs, dampers, toe and ARBs have a more limited affect on handling compared to real world. Kind of related to the LSD comment, why would the LSD be such a super tune yet put springs at softest front and stiffest rear and a car with understeer will still understeer. If I did that in real life, my car would be uncontrollable. The same is true with dampers, toe and ARBs. Maxing or minimizing settings should provide more results in the game than they do.
Did I miss any settings? In my opinion, very few of the GT6 settings are really real world.