Tape along the ceiling and trim. Place drop cloths on the floor.
Paint along the edges of the wall with a 3-inch paintbrush. Roll the paint along the edges to blend the brushed-on areas before they have a chance to dry. Apply the paint to the walls by rolling it on in different directions. Use curving, overlapping strokes.
Hold a clean roller cover in your hand, with the nap flat against the wall, and sweep through the wet paint. Use the same curving motion to create a random, overlapping pattern. Carefully blend the edges and adjacent walls.
Allow the paint to dry. Finish the walls with the top coat or decorative painting technique of your choice before removing the tape.
Wash the brush and roller covers with warm water and soap.