if car running, listen for back fire or idle not being smooth. if engine starts right away and running good, ask for test drive. what your looking for here is any issues with tranny(try down shift:if it catches right away then tranny should be fine), the wheel bearings(any squealing or binding will be evident), brakes(they should respond emmediately), ecceleration(take out on the freeway), suspenssion(should be tight), steering.
before test drive, ask to check the oil and tranny fluids. if muddied or milky in coluor, some thing bad in the engine(repair cost more than vehicle value:walk away).
if your satisfied with asking price considerring the cars condition, and are considerring the buy, than be sure to take the VIN# and order a carfax report on the car(make sure there are no liens on the car).
if you are not sure what to look for(as far as car condition), than take it to an auto shop for inspection. it's worth the cost to know what you are buying in to.