Cut your filler with 80 grit. Work your way to 180, prime. Block again, most likely will need to prime again. Wetsand with 400-600 (all depends on what you like, everyone has their own ways of doing things). Lay your base and clear.
This is just a quick way of telling you and it's about 2:00 in the mourning so I am tired and may have left some things out sorry.
Buy some 36 grit, 80 grit, 180, 220, 400, 600, 1500, 2000. That is what I use. My process may be different than some here or may be the same, we will soon see once they post their oppinion. The best person on these forums for paint help is SprayTech, I have learned lots from him.