Recommended Surface Prep
The surface to be painted should be dry and free of any dirt, chalk, grease, oil, loose or peeling paint or other foreign contaminants. Remove dirt, grease and other contaminants by washing with a detergent solution, rinse thoroughly, and allow the surface to completely dry. Areas that need special attention are doors and doorjambs that come in frequent contact with hand oils. Repair/Caulk all cracks and surface irregularities with putty or a sandable wood filler. Glossy enamel finishes should be sanded to a dull finish, dusted, and then primed with the appropriate primer.
Always prime all new or bare wood with an enamel undercoater and sand between coats.