......."What the hell??!!"
OK, we have a couple coats of paint on. Some of the pros refer to this as "pre-paint". Now I need to "de-nib"......get out specs of dirt, bugs, runs, sags, all the bad stuff that happens. PLUS....paint lays out nicer on PAINT, than it does primer. Grab a sharpie, and color the panels. This helps you SEE where your sanding so you just get the surface and don't get too deep in any one area. Then, get out your 400 or 500 grit WET sandpaper. Mix a bit of carwash or dish soap into the water to help the paper glide on the surfaces. Grab a soft block and go to town! You can see the "orange peel" in the marks. I like to go around EVERYTHING lightly, then rinse it off.