A stud gun works great for little stuff if you have one. If you don't, nothing at all wrong with tacking something (really anything) on there to tug on. I've welded some pretty sizable "tabs" onto heavily damaged panels in order to pull them back into shape while simultaneously working high spots with a hammer. Cut or nip close with a wheel, grind flush, and your done. No way will I ever drill another hole for a screw.
Another more specialized approach is using long specially bent rods to reach back into such areas from the nearest accessible place and carefully levering the dent outward. Check out PDR or paintless dent repair on You Tube. This takes quite a bit of finesse and patience, so it's not for everybody. Then again, bodywork in general isn't for everybody either, I guess.
