Check if the steering wheel is vibrating under breaking and around 50-60mph. Check the rust at the bottom of the doors and under the car. Check the play in the steering wheel, check that the speedometor needle doesn't shake. Check the the heating, A/C and fan speed is working fine. Check that the car is not overheating... Drive over bumps (very important) and check for noises, steering vibrations and good shocks. And the others obvious things : windows, sunroof...