Hey Kog. I've got a few pointers.
-Make sure you clean the gun very thoroughly to remove all grease and grit. Rubbing alcohol works fine for this.
-I find suspending the item to be painted (by a wire hanger, piece of cord, etc.) is generally a good idea.
-If the metal parts on the gun are already hot, the paint "bakes" on, causing all the chemicals and aerosol to evaporate, giving a tougher finish. A few minutes in the summer sun before you start painting should be good. This will also help evaporate any alcohol remnants left from degreasing.
-Heavy paper or light cardboard and a utility/exacto blade work well to make inexpensive stencils.
-I like the krylon fusion camo paints (sold at wal-mart, ace hardware, etc.) for most applications. It bonds well to plastic. I've also had luck with Aervoe (who makes about a dozen awesome colors) and BLP paint. Both of which we sell at Allied Surplus.
-Plug your barrel and magwell, tape off your sights, and do a test run on something not important. I usually paint on cardboard, then another on a magazine before paint ever touches my guns, just to make sure.
If you wanna do something fancy, i.e. digital, multi-cam, etc., PM me. I can definately help you out with that. I've got a few inexpensive techniques I'm willing to share.