You can find stencils at decorating and craft stores. For a more custom design, you can create your own stencil. First, find a design you like from books or wallpaper sample books. Using a copy machine, enlarge or reduce the design as needed. Then trace the design onto a 7-mil Mylar sheet or a clear plastic file folder with a marking pen. You can also use the copier to transfer your design onto clear acetate. Because acetate and Mylar stencils are transparent, you can see the previously applied colors. This makes it easier to align the pattern as you move the stencil along the surface in Step 6.
Make extra copies if you are making a separate stencil for each color. This will also let you bend or cut the stencil as needed at corners. Using a craft knife carefully cut out the "inside" of the design so the paint can be applied through the stencil to the wall. Stack the stencils together and use a hole-punch to create registration marks (see Step 4) in each corner of the stencil. These act as a guide to keep your design consistent.
Bring a dimensioned sketch and some fabric samples as you shop for stencils and paints. This will keep your interior design consistent and make sure your new stenciling complements your existing décor.