The parts of this model that I'm hoping to get a really good paint finish on get carefully trimmed and sanded to remove imperfections. Then the whole thing gets scuffed with 800 grit paper, and washed again with a toothbrush to remove dust, prior to a coat of primer.
I like to stash little bits of lead inside of parts on a scale model. You don't want to over do it, but it gives the result a nice hefty feel.