I think there have been a lot of good advice, but some that will get You into trouble very quickly...1. spray Your high build primer on, 3 coats, then after the primer flashes, spray on a very light coat of any color just so it contrasts the primer color, then when dry, if You don't have a inline sander, then use a board sander using 80 grit paper start sanding the work area, the first thing to go will be the guide coat, it will show you the high spots as well as the low spots...It will also show You if maybe might have to tap the high spots down, then re-coat, if necessary.
Next, use 220 or 240 grit to re-block...I had a body shop for 30 years, and taught metal finishing, and did show car painting for cars that were in the auto shows. A total of 55 years experience...good luck.
