Cover the floor with drop cloths. Tape around the ceiling and trim with low-tack painter's tape.
Select a paint color for the walls. Paint tends to look darker and brighter on the wall, so it is always a good idea to paint a sample directly on the wall before purchasing larger quantities of paint.
Apply the paint around the edges of the walls with an angled brush. Roll out the rest of the walls with a roller. Smooth out any overlap marks or drips. Allow the paint to dry. Apply a second coat of paint, if necessary.
Mix stencil colors using acrylic paints. For 3D effects, make a few shades of each color. Stencil paint should be fairly thick to prevent runs and drips, so don't dilute the acrylic with water. Add a few drops of matte medium to thin the paint, as needed.
Spray the back of the stencil with spray adhesive, so you will not need to hold the stencil up while painting. Decide on an arrangement for your stencil design. Start a border in a less noticeable corner to allow you to finesse the spacing of the final few stencils. Place your first stencil in the middle of a prominent wall if you are creating an all-over, random pattern.
Dip your stencil brush in the paint just to barely coat it. Blot off excess paint on a rag. Apply the paint to the exposed wall using a gentle pouncing motion. Pay attention to hit around the edges to get a clean, crisp design. Apply lighter paint in the center of your image to create the illusion of form. Blend the lighter and darker shades by pouncing where they meet with your stencil brush.
Carefully peel the stencil off the wall. Wipe off the back with a damp rag, if necessary. Reposition the stencil and repeat the painting process. After stenciling several images you will need to wash the stencil off and reapply spray adhesive.
Wash all tools and brushes with warm soapy water.