Draw the outline of your design on a piece of cardboard, using a marker. The cardboard should have a 5-inch edge around the design to account for splattering.
Cut out the cardboard inside your outline with a utility knife, leaving just the outline of the design that you can fill in with paint. If you are going to use more than one paint color, cut a new stencil for each color.
Place a strip of masking tape on each side of the stencil so it sits halfway off the piece of cardboard. As you move the stencil across the floor, the tape will keep it from shifting as you paint.