i like a rubber mallet, right on the center of the dent, or where the crease is.
you'll need to take off any "covers" that prevent you from getting to the "other side" of the dent.
then just whack it back.
if there is no crease in the dent, or a flat enuff spot. get it wet then use a toilet plunger to pull the dent out.
note: any dents you pop out will come back easy.