Break your gun completely down. Absolutely gut it as far as you can and keep your internal parts and hardware in a jar, or coffee can, or even a plastic bag.
Then, get all the old paint off. It may have oils absorbed into it that will affect your paint setting correctly. I used a wire wheel to clean off my parts. Some people use bead blasters.
Then, tape off all the internals of your housing. Mine is still factory black on the inside. Get every little hole. I used a coat hanger to hang my parts.
After that, if you're going with a gloss-job, you need to spray on a coat of primer. I prefer two, but that's just personal opinion. One good coat would probably work. Then, after its dry (the can says 5-15 min-I like to give it 45 min to an hour), lightly spray on your gloss. If you don't think you got a spot right-give it ample time to dry and then come back for that spot on the next sweep. I usually do 5 or 6 sweeps with time in between. Then let it dry for 24-36 hours before attempting to assemble the gun. I work very slow with gloss paints because its so easy to screw up.
If you're gonna go with flat paint instead, after you have the old paint off, you can get away with doing a coat of primer just to be safe, and then do three or four coats of flat. I like the way it looks better, and how much quicker it is. You only need about 15-20 min between sprays for your avg paint job. Then, after an hour of setting, its good to go.
The paint I used is thicker than your avg paint and you can still see the serial number just fine.