1) Replace all bushings as well as new shock/strut/spring...or coil-overs. etc.

2) More torque a car has the easier it is to drive smoothly...

3) Keep all rubber trim conditioned with Turtle Wax ICE Total Interior Care or comparable then glass cleaned with Invisible Glass by Stoner.

4) It's called undercoating. I'd suggest cleaning then spraying with Rustoleum paint to help prevent the rust from spreading then spray the rubberized undercoating. Both available from everyday parts stores. http://www.duplicolor.com/products/undercoating.html

5) OEM plug wires? Valves been adjusted? What car? EG hatchback? What engine?