Start by unplugging the toaster oven, and taking on the easy-to-dump debris first. Simply shake any crumbs or other food particles into the trash.
Next, remove the rack and pans, and spray them and the crumb tray with all-purpose cleaner. Use a non-abrasive scrubbing sponge to get off. Rinse, and let air dry.
To tackle the oven itself, spray a scrubber sponge (or a regular sponge, if the interior is non-stick) with more cleaner. Never spray appliances directly. And steer clear of the heating elements inside. Wipe the exterior as well, including the glass door. Use a vinegar and water solution on the glass.
Be sure the oven's dry (wait about five minutes), before plugging it back in.