Most manufacturers of body hammers will have a door skin variety hammer, the one side is angled to fit around inner door obstacles. The opposite side is straight for when you don't have the obstructions. Either face has the "leading edges" in a radius so that you don't have to worry about the hammer face having sharp edges that would leave creases on the flange as it's folded.
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Note the dolly used is all but flat, here you need to keep the dolly tight to the skin at the point of the crease, to keep the fold a tight and crisp as possible. Even though the door skin may appear straight at the bottom there is indeed a crown and the dolly should stay tight to the part we're folding. Note in the following picture the flat dolly does not conform perfectly to the crown of the door. Here we want to ensure the dolly is touching at the point adjacent to your hammer strike on the flange.
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You can finds all sorts of tools and gadgets to help out with the installation, here is the "Door Skinner".
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There are attachments for air chisels, and the list goes on for the next thing since sliced bread for installing door skins. At the end of the day, I feel someone who does not do this every day should choose a slow and methodical method, ie: the door skin hammer and dolly, so you can closely watch and monitor the progress. Powered tools make short work of something, but if an alignment is off, they're also quicker to make a blunder. Lastly, I would suggest epoxy priming the inside of the door skin and entire inner door separately.
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Once paint is cured, assemble, fit to vehicle, and some slight twisting may be needed to get optimal matching of body profile. After tweaking to provide best fit, then do your plug welds. Now mix up some more epoxy primer and use a turkey baster or other similar device inside the door to seal the seam, both ends and bottom.
