check the body panels and make sure everything lines up with each other. check the tires...to see if there is sidewall wear. if there is...then u know the car has been driven semi hard.
check the gearbox to see if all the synchros are working well. check the radiator support beams up front to see if the car has ever been crashed.

check for mods. coilovers, springs, nuts on the engine holding the top hat (if these are worn...suspenion has been changed).

ask lots of questions

 

Well obviously drive the car before you buy. Check all the normal things. Ask for maintainence records. And most importantly be vary wary of any car that appears to be modified. That especially goes for heavily modified cars and cars with cold air induction. Low milage is also a good thing. And if you have access to a mechanic it wouldnt hurt to bring it in.