check cv axles to see if boots are broken (axles will click or car may shake under acceleration), check tie rod ends, check tires for excessive wear, push down on the front/back of the car and see how much it bounces (if it bounces up and down several times the struts are bad), check for exhaust leaks, and obviously if the car stumbles or bogs or has a hell of a time starting you might want to have it checked out before you buy it by a mechanic to make sure the motor isn't on it's way out.