for the sanding part, start out with something gritty, but not to abrasive, like a 60 or 80 grit sand paper. Then after you've removed most of the paint, you have two options, you can use a primer that will mask deep scratches and it will get a good bite in from the grittier sand paper, granted, this method while assuring the best hold for the primer, might not turn out the smoothest, but that depends on how many coats of primer and paint you use. Alternatively, after you go over it with the 60 grit, go over the case again with some much finer grit paper, 120 or so. Then just as Big B described, and put down like two or three coats of primer, but make sure to sand the primer with the finer grit paper, then on to paint, probably three coats, then if you want it to last a little longer, get some clear coat, and you'll need like at least four coats to spread the clear evenly. On a final note, to make the job look nice, it might be a good idea to practice on something first, rattle cans are kinda funny to use, but if you practice the proper technique you can achieve really good looking results, but as a ground rule, just remember, light coats. Oh yeah, make sure to tape off anything you don't want to get overspray on.
