Sand, then primer, the flat black, then gloss black. That's the best way to do it. Don't spray it on thick either, mist it, let it sit for an hour, mist it again, sit for an hour then mist it the 3rd time. Let it sit overnight (12 hours) then do the same thing with the next step. If you do it right it will take you 2-3 days but will look good. If you rush it, it won't look as nice.