I want to repaint the bodywork
A better article than this one
Think hard before you get started
Painting is labor-intensive. Unless you've done it before, figure out about how long it's going to take you, then multiply that time by 5-10X. It involves a lot of tedious, repetitive sanding and prep work. So, plan on being patient and taking your time. That, or you can just spray truck bed liner on it like one of our Mighty Leaders and be worry-free for years.
The painting process
The best way to do this is with automotive wet-dry sandpaper. You can find this in any automotive store. First thing, use a fairly coarse grade and wet sand the part. A crude but effective way to do this is to put the part in a large trash can filled with water. If this is impractical, just be sure to keep the part wet. A hose set to a slow dribble works well.
You don't need to worry about being mirror smooth at first, just don't press too hard or you will make lines that will be difficult to hide later. Once the old paint (and the clear coat that is on top of the paint) are removed, prime it. Hanging the piece with a hanger is a good way to go. Be sure to prime the whole piece at once. After letting it dry for as long as the can says, apply a second coat. After 15-20 minutes, wet sand it again. Unlike before, you're now striving for a mirror-smooth surface. When you take off too much primer in a spot, and you will, reprime the whole piece. Don't do spot priming. It could likely take 7 or 8 coats to get it perfect. Also, applying the primer needs to be done one coat after another, so make sure you have plenty of time.
After 24 hours of drying, the easy stuff is all that's left. Use paint from the same manufacturer of the primer. Get the primer, paint, and clear coat all from the same company. Spray the paint 10-12 inches from the piece, using long strokes. Move your whole arm and not just your wrist. You've likely seen commercials for body shops that show the guy with the spray gun moving the entire length of the car without stopping; that's what you're going for. Be sure to overlap the passes, but don't spray too long or too slowly in any one spot, or else drips and runs will form. If they do, let the paint dry a bit beyond being tacky and wet sand the runoff. Apply 4-6 coats of paint.
After you get the paint exactly how you want it, you need to seal it using clear coat. If there are any problems with the paint, now is the time to fix it. Apply the clear coat in the same manner as the paint. Apply 5-7 coats. Plastic parts don't need to be buffed the way metal parts do (like gas tanks). Any automotive site should have articles on how to paint metal and get an excellent mirror finish.
Information on paint types; which kind of paint to use