do good metal work with planishing hammers, shrinking disks, plastic mallets. All that stuff takes time, experience, and to know how metal works(easy part. You can also use lead or synthetic lead to use as filler. Either that or you have a bondomobile, a primermobile, or a wavymobile. I'd love to do all my work with shrinking disks and true restoration tools but nowadays no one has the money to pay for those kind of jobs. My advice is, if you have the time and money and the car is gonna be worth while why not? If you don't get the perfect results you're looking for than it's that much less filler to apply, but you should be aiming for a straight finish to where you only need a primer to level it.
Anywho, we use 3m Platinum filler, various urethane/polyurethane primers, and sometimes we use z grip to fill over huge manholes.