Hold the stud finder flat against the wall for a few moments in order to calibrate it. Holding it in place helps the stud finder measure the depth of the wall.
Keep the stud finder flat against the wall and move it from left to right.
Watch the light on the stud finder. On many models, when you near a stud, a red light will rapidly blink. When the stud finder is directly on a stud, the stud finder will make a sound and a solid green light will appear.