Some tips for painting brass would include roughing the surface up with methylated spirits mixed with sand and applying a red oxide primer. Both of these steps help make the surface more smooth and gives the paint something to adhere to.
Another tip for painting brass is to first clean the surface with thinner. This helps to remove not only dust and debris that may ruin a paint job, but also removes the lacquer that many modern brass fixtures are coated in. Additionally, you should always first apply a thin coating of paint, called a basecoat, and wait for that to dry before applying the main coat of paint.