sand sand sand...then vacuum or use a tack cloth. then prime with an oil based primer/sealer. sand again....top coat with latex semi-gloss...sand again...apply second coat of top coat. I recommend removing all the hardware before painting...yes, this includes the hinges...it's more work, but it's worth it.
have the paint store tint the primer to the same color you plan to use as a topcoat, this will save time and coats.