Header paint is applied the same way as you would paint, and the secret to painting anything is to prepare the surface for maximum adhesion. Properly mask off any surface where you do not want the paint to stick to and carefully remove any contaminants on the actual surface that you would be painting.
The first step is to remove any old paint on the surface if there are any; this would involve an industrial-grade paint stripper or sanding, whichever the case may be. Next, ensure that there are no oils or chemicals on the surface to ensure proper adhesion. Remember that each product may vary as to how far the sprayer should be from the surface or how many minutes you need to wait before each coat. Because of this, read the fine print on the can of product you will be using for any special instructions in the application process. Once you have done that, you are good to go.