DO back up extensively. A common mistake among nonprofessionals, says Pike, is inadequately backing up wedding files. This includes immediate Internet, hard drive, and DVD backups, but also instructing the wedding couple that they, too, are responsible for backing up digital wedding pictures. Also, as you pull full memory cards from your camera, store them securely, all in the same location. "One of the worst things that can happen is losing a memory card," warns Kwan.