Measure your fence and draw it to scale on graph paper. Sketch your design on the paper.
Mark your sketch in a grid fashion. Note the center of the design both vertically and horizontally. Start at one side of your drawing and score the design in even increments. For example, note every 5 feet. If your graph paper scale is 1 inch to a foot, then mark every 5 inches.
Prepare the surface of the fence by washing it with a grease-cutting detergent. If the fence has never been painted, apply two coats of primer paint. If the paint is old, sand it well and apply two coats of primer.
Mark your fence with tape to correspond to the center and other major measurements. Use a watercolor pencil to sketch the design onto the fence, using your graph as a guide.
Paint large blocks of background color first. Work from the back to the front of your design.
Add small details last. In most cases you will want the background to be dry before you add the designs in the foreground.
Apply a topcoat to seal and protect your design. One or two thin coats of polyurethene or lacquer will work well.