Wow, big question. The suspension, stablizer and spring rate determine that. The heavier the car I set the suspension to stiffer (higher number) and keeping suspension and stablizer around the same amount. Spring rate is a bit more tricker and needs quite some adjustment. Go with lowest setting and set it higher and see what kinds of effects it has on your specific car.

RWD, FWD, AWD or MR all determine if the front or back suspension should be stronger/weaker.

Please find a faq from gamefaqs.com and they should explain all that to ya.