Body and paint are a learned skill that requires lots of hands on experience.
Truer words were never spoken. I always have farmed out body and paint work on my projects until my finances forced me to tackle this job myself. A couple of things I have learned that might help. There are no shortcuts, at least for novices like myself. If you want it to look perfect you have to follow every step the experts recommend- see the above post re: block sanding. The longboard is your friend. I purchased a couple of highly regarded DA sanders for doing the finishing work. I used one of them for 5 minutes. Even the fine finisher removes material faster than my skills can deal with it.
I cannot feel the kind or surface irregularities you describe that show up after painting. The surface may feel perfectly smooth but what a disappointment after painting. When I use a filler on a curved area I usually have to sneak up on the defect little by little. The block sanding will keep taking out the top of the defect until the sides are built up enough. A skilled body man can probably eyeball this to some extent and get to the final faster. Without more primer and a guide coat, repeat as often as necessary, I would never get the surface perfectly flat.
Finally, what helped me most doing body and paint work was to quit focusing on the goal (completing the job) and getting into the art of making the surface and paint as good as I could get it. This has turned out to be surprisingly rewarding to me despite many, many screwups and frustrations.
Chuck
