i do this for alot of people and make money off this haha. but uhm yea
take preferrably a strong compound like goo off (home depot carries it) and wipe any dirt off of the light surface.
depending on if you want purple reverse lights or clear (which look better) take masking tape and a razor and cover the area of the reverse light.
take 800 grit wet sandpaper and wetsand the tail light so it looks really dull but yet smooth. make sure its clean
start off with a light coat about 10'' away. spray and stop. repeat so you dont get any drip.
do about 10-20 layers. let it dry for a couple hours. if you have any drip, this is the time to fix it by wetsanding it. if not, take clear coat and do about 5-7 coats.
let it dry. for a flat black look which actually will look good and not as dull as you think, keep it. but wetsand it with 2000 grit and your done.
or to get a glossy finish to match the paint, after you clearcoat everything, wetsand it lightly with 2000 grit, take a buffer and buff it with a light buffing compound about 3 hours after it drys.
ive actually gotten good at this. anyone can do it and its affordable. but once you do it so many times, yours will stand out from someone who just sprays and puts it back on. if a local shop doesnt carry it, you can get it on ebay.