Pinpointing a stud is part art, part science, especially on thick plaster walls. The science part comes in sweeping a wall with a battery-powered or magnetic finder to locate the approximate location of a support. Measure 16 or 24 inches to either side to find adjoining studs. Confirm their centers with the stud finder. The art part comes in verifying that you've hit the mark by tapping the wall with the handle of a screwdriver. A hollow sound means you're between studs; a thunk indicates solid purchase. With drywall, you can also wave a flashlight across the surface to scope screw holes or drywall tape, telltale signs of a stud.