When cleaning up line art images with the Pencil tool, you can spend a lot of time going back and forth to the Toolbox to switch your Foreground color to black (to fill in missing pixels) and then to white (to erase pixels that shouldn’t be there in the first place). It does help if you use the keyboard shortcut D to set your Foreground to black, and then X to make white your Foreground color, but there’s actually a faster way. Once you select the Pencil tool, go in the Options Bar and turn on Auto Erase. What the Auto Erase option does is pretty neat—when you click the Pencil in a black area of pixels, it paints white; when you click it on a white pixel, it automatically paints black. It happens automatically—so you never have to switch colors again—saving you a ton of time, travel, and keystrokes.