Resist the urge to pound away at the center of the dents. Start at the edges and work your way toward the center, using a dolly block or maybe a heavy block of wood to brace the metal as you gently tap the edges of the dent outward. Be patient, and remember that the metal has a "memory"- - - -it wants to go back to its original shape. There are three basic shapes that form all body panels- - - -"crowns", "ridges", and "flanges". The dented areas you're dealing with are mostly of the crown variety- - - -a flat piece of metal that has been stamped in a big press and stretched into a curved surface. You're trying to coax it back to its original shape, without stretching the metal further than it was originally. Sometimes that's impossible to do, as the bending force that caused the dent has stretched the metal beyond its ability to resume its original shape. As it approaches that shape, the dented area will begin to spring in and out, a problem known as "oil canning", named after the old-time hand-held oiler with a stretched bottom that allowed someone to squirt a small volume of oil out of the tip. To repair a springy surface it might be necessary to shrink the metal by heating a small spot red hot with a fine-tipped acetyline torch and then quenching it with a water-soaked rag. That's a skill that's developed over long-time experience. There's not much way to teach the process, so practice on a piece of scrap before trying it on a part you can't replace.
Once the metal is close to its original shape, a process called "metal finishing" is used to fine tune the surface. The contour is filed or scuffed with a sander, and high and low spots can be raised or lowered by careful metal bumping to achieve a smooth surface. A properly straightened and metal-finished part shouldn't require more than a thin skim coat of body filler, or possibly none at all, before being primed and painted. Have fun!
Jerry
