ok well, i used 600 grit sandpaper because its already very smooth and what u want to do is scuff it all up to get good adhesion or something like that. after i sanded it all down thoroughly and then wiped off all the dust with a damp towel i sprayed about 3 or 4 light coats with krylon fusion satin black satin.
thats pretty much it, ive taken my headlights apart about 4 or 5 times since then and the paint is still holding up great. no flaking, no nothing.