To paint over stained wood, use 150-grit sandpaper to sand the surface. If the furniture looks glossy, sand until the surface looks dim. If the furniture isn't glossy, just sand out the rough spots. Remove all the nails and hardware from the furniture and coat the furniture with wood primer, allowing it to dry completely for about an hour. Paint the furniture after this.
Before starting to work on the furniture, cover the floor with tarps, clear the area around the working space, and collect and arrange all the materials you need for the job. Use a cloth to wipe down the furniture, ensuring there is no dust or dirt left on it. Eliminating the glossy look of the furniture is important, as it ensures that the paint adheres well to the wood surface.
Use some spackling to fill in any holes from removed nails, as you need a smooth surface for painting. If the piece of furniture has drawers in it, take them out and paint them separately. When purchasing the wood primer for the job, consult with the painting professional at the store about the type of primer you need. Tell him what kind of stain is covering your furniture and what kind of paint you plan to use.