hey, yeah, i rattle can those mirror myself... One thing is for sure, take your time... don't get anxious and just fly through the prepping part... it'll be a PITA if it started chipping and you have to do everything again. I'm referring to my door handle about the crappy prep job because i basically just do a quick sanding and on goes the base coat and nothing else and now it's chipping and i'm using touchup paint on it lol... gonna repaint it when it gets warmer.
Anyway, to prep the mirror (I use duplicolor), you need to sand it down "smooth" and i do mean "smooth". Mine was the grainy plastic texture originally and i had to use about 300grit sandpaper then, 500 then 800 then 1200 and then 1500. Once you're done then wash it clean. Take your time with the sanding, the smoother it is, the longer the paint will stay on and the smoother it would look when finished.
Then spray on the primer, about 4 coats, or to the point where you've completely cover it so that you don't see any dark spots from the black plastic. let it dry. Then sand it gently with 1500 grit to get it smooth and rid some of the dust that stick to it when drying. I used a hairdryer to speed up the drying though... (preferably indoor to reduce dust). Then spray on the base coat. Oh yeah... depending on what color your car is, if it's light go with white if it's a dark color go with black, and if it's medium color, go with grey. I vote white if you're going with a silver car. Then spray on the base coat. Again, the number of base coat depends on the color of your car. More layers = darker shade. For my silver car, i only put a minimum amount, just enough to cover it in order to get a light silver color, other wise it gets a little darker than the rest of the car. once you're finished, let it dry. Then sand it "gently", you just want to get the roughness on the surface off, they call it overspray. You do not want to sand down to the paint that you want, just the roughness. Then after that blow off sanding with hairdryer and then clean the surface with a wet cloth gently. Then next comes the clear coat. This coat you put as much as you can

the more, the thicker, the glossier. I put 7 layers, but the more the better. Just depends how much patient you have to apply that many coats.
P.S. take your time between layers. don't let it flow... if it flows you're screwed and you have to let it completely dry like a couple of days and then sand it all down before starting over. so like i said take your time.