Apply a primer to the clean surface with a paint roller or paintbrush before you begin painting. This will reduce the number of paint coats you need and will help you achieve a smooth finish.
Sand the dry primer with a wet extra-fine-grit sanding sponge until the primed surface feels smooth when you run your hand over it. Keep the sponge and the primed surface wet as you sand using a spray bottle full of water. Dry the surface thoroughly when you finish sanding.
Apply a coat of paint to the surface with a paint roller or a foam brush to minimize brush strokes.
Sand the dry paint with an extra-fine-grit sanding sponge using the same method described in Step 2.
Repeat Steps 3 and 4 to add a second coat of paint.
Apply two to three coats of clear polyurethane to the surface, sanding between each coat to ensure a smooth finish.