Sand it by hand or with a power sander, then wipe it dry. Use a latex primer, 2 coats is best, and allow it to dry between coats. Then apply the latex paint. I've some hard to paint with my Critter spray gun. To the primer i make use of http://codymevjl.blogpostie.com/12713679/about-what-is-the-most-durable-paint-for-kitchen-cabinets