Scour the yard or a nearby park for leaves, then place your favorites inside a thick book for 24 hours to flatten before affixing them to pretty pin boards. Some kinds, such as pin oak and southern magnolia, keep their color naturally; others need a little help. David and Leanne Kesler, co-owners of the Floral Design Institute, in Portland, Oregon, recommend an old-fashioned trick: Iron them. Using medium-low heat, press leaves between two sheets of wax paper until the wax melts, bonding the sheets together. Separate the two pieces; the leaves should come right off.