surface
fill the voids with whatever filler you're using most guys on this site use evercoat. sand the surface to like 80 or 150 grit. then I prime with a epoxy sanding primer I'm using the ppg 7650 gray primer. cause I know that we are going to use ppg finish primer and paint to finish. then usually you can sand out the primer with like 220 and be ready for finish prime and paint.
happy building
Erik