Mask or tape off the perimeter of the ceiling where it meets the walls to be painted, using masking tape or painter's tape. Use a ladder if you cannot reach the ceiling. Apply the tape as close to the wall as possible without getting it on the wall. Rub the tape down to prevent gaps underneath.
Open the paint can, and stir it per the manufacturer's directions. Pour some of the paint into a paint tray. Set the paint tray on the ladder's paint-tray holder if you're using a ladder.
Dip the fuzzy part of a paint pad into the paint, keeping the pad parallel to the paint for an even application. Remove the pad, and allow it to drip back into the pan for a moment.
Hold the paint pad parallel to the wall. Run the paint pad left to right -- or right to left -- starting in a corner or edge of the wall and moving the pad in a smooth motion along the top of the wall where it meets the ceiling. Hold the pad so that the paint on the uppermost part of the pad coats the top part of the wall completely.
Dip the pad back into the paint, and apply a new line of paint where you left off. Continue doing this until there's a band of paint along the entire top of the wall where it meets the ceiling.
Remove the tape from the ceiling.
Finish painting the wall or walls, using a roller or your preferred painting method. Overlap the paint band near the ceiling slightly, but do not go over the entire band. The band eliminates the need to use a roller near the ceiling.