[genkichild]

Hammering can work. If you cant get to the backside of the place where the dent is, you could go old school and drill a hole, put a screw in there and pull it out (seriously). Then putty up the hole (like with bondo or something), sand it out, and paint it.
If that is too scary, you could try one of those glue or suction dent pullers (like Ding King). Some people get lucky and it works. Kinda depends on the shape of the dent, if it is on a corner, etc.