Trace your image on to tracing paper, then center the paper over acetate or oil board (both are available at your local craft store).
Cut the shape out of acetate or oil board with a craft knife. This will be your stencil.
Then, using low tack tape, a pencil and a tape measure, use your stencil to plan your pattern out on the wall. Be sure to measure carefully to ensure proportional placement around windows and doorways.
Using your stencil again and again across the wall, apply colorwash with a few parts of the lightly dampened applicator cloth.
After colorwashing the stencil shapes, let dry. Then apply a classic colorwash over the entire wall.