If needed, patch and repair any cracks or holes with joint compound. If the paint has a gloss finish, lightly sand the walls with fine-grit sandpaper. If the walls are greasy or particularly dirty, use a degreaser to remove the grime. Wipe the walls with a damp rag to remove any dirt and dust, and let dry. Before painting, apply painter's tape along the edges of the walls, and place drop clothes on the floor and any furniture in the room.
To cover bright or dark colors, use a gray or tinted primer. Select a color for the tint that is similar to the final paint color. Apply the primer, and let it dry according to the manufacturer's instructions. Add a second coat, and let it dry.
Once the primer is dry, paint the wall in the color of your choice. Once the first coat is dry, add a second one. Depending on the quality of the primer and the paint, you may need to apply three or more coats of paint. Allow each coat to dry before adding another.