Frist thing you need to is get some scotch brite pads. You should be able to get them at any auto part stores. Then rub the metal intill it has a fine texture to it. After that blow all the dust off of it. Or you can use a wet rag. Then apply two coats of primer. But us a primer thats color is close to the color you are useing. Let the coats dry as the can says. Then take the color you want apply all the coats in a thin layer and let them dry to what the company says. Now if you want you can apply a clear coat. This is how all body shops paint all types of metals. By the way any type of spray paint will work. What are you painting by the way?