To prepare wood paneling for painting, examine the wall for any holes and other uneven areas, and smooth them out using joint compound and a putty knife. Sand the panels using a fine-grit sander to ensure better paint adhesion. Clean the panels with tri-sodium phosphate to remove dust, rinse the panels with water, and allow them to dry completely. Fill the grooves in the paneling with joint compound, allow it to dry, sand them out, and remove the dust.
After preparing the wood panels for painting, start the paining process by applying primer to the panels. Make sure to place protective tape around the area you're painting before applying any products to the walls. Apply a thin coat of primer to the entire surface, and let it dry completely before proceeding. Make sure to mix and aerate the primer according to the manufacturer's instructions before applying it. Sand the wall lightly, and remove the dust before applying paint.
Start painting with a brush around windows, edges, doors and the ceiling. After that, paint the rest of the walls using brushes, rollers or paint sprayers. Try to make the paint coat even throughout the area, and let it dry for a day. Apply however many additional coats of paint you need. To achieve better results, sand the panels every time before applying a new coat of paint.