tomsteve wrote:i start at 800 grit on a block. take it down until the filler is just about gone- as in theres more paint showing than body filler- then switch to higher grit
Yep, this is the key.
I like this method because it gives you visual cues that can be seen when wet sanding. When wet sanding you can't see that shiny area next to the run that '68 mentions unless you squeegee off. Once the filler is gone you know you're in danger territory, more so on curved panels where the stick might not work.