I had these metal bins that I wanted to paint, (see post here on the completed project) and so this is how I did it. No I didn't research the "right way to do it", I just did it my way.
1. Empty out bins of objects and dust off inside & out.
2. Create space in garage to be able to spray paint the project. Lay plastic and put items on plastic.
3. Spray with a matte grey metal primer.
4. Let dry.
5. Spray your desired finish color.
6. Let dry.
7. Touch up or spay 2nd layer of finished color depending on what look you are trying to achieve.
8. Let air dry overnight.
9. Bring back in and setup in place and put your
junk stuff back in the bins!
10. Enjoy your completed project that took you 6 years to do!