Move the furniture out of the room or toward the center of the room, away from the walls. Remove knickknacks and items on top of the furniture so they don't become damaged. Cover the floor and furniture with dropcloths.
Sand the walls and ceiling lightly with 120-grit sand paper. Use an extension ladder, sanding pole and face mask for this job. Sanding prepares the walls for the new coat of paint so it will adhere better. Start with the ceiling and work your way down the walls.
Clean the walls and ceiling well with a rag moistened with warm water. A mop will likely be necessary for the tall areas and the ceiling. Rinse often so you do not move the dust and dirt around, but instead get rid of it. Clean any trim you plan to paint as well.
Select a high-quality paint with an added primer so you don‘t need to apply a separate coat of primer. Choose a color that closely matches the existing paint color for rooms with high ceilings so you do not need to apply several coats of paint to cover up the old color.
Paint along the edges and corners with a paintbrush. You can also use a miniroller instead. If you are painting the ceiling a different color than the walls, carefully paint along the edges, keeping the bristles on the dry side and using a steady hand to make clean lines. Otherwise, you will need to tape along the top of the wall, which will be difficult in rooms with high ceilings. Use an extension ladder for this step.
Paint the ceiling with a roller and extension rod. Paint in rows that overlap one another. It is difficult to paint a ceiling with large W-shaped motions as you can the walls. Paint the walls in a similar manner as the ceiling; however, you can more easily make large W-shaped motions for complete coverage.
Paint the trim and any woodwork with a high-quality brush after the last coat of paint.