Clean the walls with a solution that contains a mild detergent. If there is mold on the walls, use a solution of one part bleach to three parts water. Allow the walls to dry.
Mark the bottom edge of the wall at several points by measuring the distance from the floor to the bottom edge and making small pencil marks.
Connect the marks by drawing a light pencil line, using a straightedge as a guide. Mark the top edge of the border by measuring down from the ceiling.
Place painter's tape on the walls on the outer edges of the pencil lines.
Place stencil adhesive to the back of the stencil and allow it enough time to become sticky.
Hang the stencil on the wall between the strips of painter's tape. Use a level to make sure you hung the stencil straight.
Create a simple palette by pouring small amounts of the paint you're using onto a plastic plate, keeping the colors separate.
Dip a stencil brush into the first color you're going to use. Add just enough paint to cover the bristle tips. Wipe off any excess paint on a paper towel.
Paint the wall by applying the paint in the correct locations of the stencil with short, quick strokes. After you've finished applying the first color, begin painting the stencil with the next color. Clean the brush thoroughly if you're using the same brush for multiple colors. Allow the paint to dry.
Remove the stencil from the first section and move it to the next section. Keep the stencil perfectly aligned with the first section.
Paint the next section of the wall and allow it to dry. Continue painting the sections until the walls are finished.
Remove the painter's tape from the walls.