Here's a good first step - Block Sanding Kit 3 Sanders-2PSA paper Guide Coat Guide coat & block sand to ID low spots. If shallow (~1/16" or less) just fill with a good quality body filler and sand using blocks & 180 to 220 grit. Two coats of epoxy primer, block to check one last time for lows & highs, and a final prime coat for any sand throughs. Watch the video on the Eastwood site page attached for some basics.