sanding help ?

[1968GMC]

I posted this question in paint and body and only got 1 responce,so ill try here. Im painting my truck this winter,I saneded my glass rear fenders with 220 grit sandpaper, then came back with 100 grit sandpaper on my paint chips( to fether them out) then resand with 220. This is what i done so far. Now I want to primer filler my fenders and resand with 320 grit then reprime with a primer sealer and sand with 400 grit.My question is is this the corect procedure or am I missing something. BTY happy newyears to all.