How do I paint over furniture that has been coated in polyurethane?

Q: How do I paint over furniture that has been coated in polyurethane?

A: The tried and true method for refinishing furniture is to strip or sand down to bare wood. Another option is to use a chemical to etch the polyurethane prior to recoating. First, thoroughly wash the surface, using TSP for heavy-duty cleaning. Etch and de-gloss the surface with 100-grit abrasive. You should see light scratches in  the old finish. Vacuum all sanding dust and wipe all woodwork with a clean, damp cloth. Using a rag saturated in Liquid Surface Preparation agent, apply the chemical to the finished wood to agitate the surface, following the directions on the container. Apply primer to the treated surface within thirty minutes.