Before blocking, make sure you put some guide coat on the high build primer. Then, here is what I do. I use 220 first. Using a cross hatch pattern, use the 220 until most of the guide coat is gone. Then I switch to 320 and sand until almost all of the high build is gone and the body is perfect. Then I put on a few coats of 4:1 primer (it wet sands beautifully). I start with 320 wet until ALL of the orange peel is gone, then I switch to 400 wet. then do the 400 until the primer is as smooth as a baby's butt. Then you can hit it lightly with 600 wet and you are done. Some will say don't use 600, but a lot of people do, and I have NEVER had any problems. The key to a good paint job is PREPARATION. Sounds like a lot of sandpaper? You will need 1000, 1500, 2000 and 2500 wet paper to color sand before polishing.