Rub the wall surface gently with the art gum eraser. By using a new eraser, you prevent smudges on the wall.
Use a clean area of the eraser to continue rubbing gently to remove every trace of pencil marking. Reposition the eraser often so you always rub with a clean area of eraser. Continue working until you successfully remove every pencil mark.
Wipe down the wall surface with the tack cloth to remove dust and debris.