I followed this process for my rear bumper and sliders, both of which were shipped raw.
Wipe down dry, then scuff the surface lightly with a 3M pad or 600 grit sand paper. Wipe all debris while dry, then clean with mineral spirits and allow to dry.
2 coats Rustoleum self etching primer, followed by 2-3 coats Ace Hardware Satin Black Enamel (both rattle can varieties). Follow the timing instructions to the tee, as mentioned above.
I went with the Ace product because my local store didn't have the Rustoleum in satin black when i did the bumper and It turned out so well, I used the same for the sliders. Very happy with how both turned out.