Before setting sponge to surface, consider what your wall is covered with. Avoid washing flat emulsion paint, which can be damaged by water. (Jeff Bishop, a technical adviser to the Institute for Inspecting, Cleaning, and Restoration Certification and the president of Clean Care Seminars, suggests a dry-cleaning sponge as an alternative.) But for gloss paint and most wallpapers (except vintage or antique ones; check with the manufacturer if youre concerned), a DIY cleaning is good to go. Its always best to test in an inconspicuous spot first.