Always unplug your toaster oven and allow it to cool completely before starting any cleaning task.
Crumb trays should be removed and cleaned in warm, soapy water at least once a week if you use the oven a lot. Excessive amounts of crumbs in a toaster oven pose a greater fire hazard than the same amount left at the bottom of a toaster because the heating elements tend to be both larger and closer to the crumb tray. Unplug the appliance first and remove the tray over the sink or trashcan to avoid leaving the inevitable spray of crumbs across the countertop. Rinse well and make certain the tray is completely dry before replacing it in the oven.
Regularly washing removable items, including the glass door, in the dishwasher will save a lot of time and effort. Removable racks and baking/broiling trays can also be washed in warm, soapy water. If there’s a lot of stuck-on food, let racks and trays soak for a while in the soapy solution before scrubbing. You may need to use a degreasing cleaner on especially greasy items. Avoid using ammonia, chlorine bleach or any cleaner containing them on aluminum or nickel-plated parts. Both chemicals can permanently darken these metals. Also, don’t use any abrasive pads or gritty cleansers on chrome-plated parts, which can be scratched by aggressive cleaning methods.
Apply glass cleaner to a cloth to clean a chrome toaster-oven cabinet. Substitute an all-purpose household cleaner (or highly diluted hand dishwashing liquid) on plastic or enameled metal oven enclosures. Wipe well with clean water to rinse, and then dry.
Like toasters, toaster ovens attract many hard-to-remove spots that get baked on by high heat. To remove them, soak a paper towel in all-purpose cleaner and place it over baked-on spots for several minutes, making sure the toaster is cool and unplugged before starting. The cleaner will help dissolve the stain over time. Follow up by cleaning the rest of the cabinet as usual.
Don’t use abrasive pads or cleansers on the cabinet exterior because it’s easy to scratch these surfaces permanently. Never stick any tools inside the oven to avoid damaging heating elements or other interior components. Don’t ever spray, or pour liquid on or into, any electrical device – always apply cleaner to the cloth, never the appliance.
Toaster ovens should be allowed to dry completely before being used. Place the appliance in direct sunlight for a while if necessary to speed drying.
References:
Don Aslett, The Cleaning Encyclopedia: Your A to Z Illustrated Guide to Cleaning Like the Pros.
Jeff Bredenberg, editor, Clean It Fast, Clean It Right: The Ultimate Guide to Making Everything You Own Sparkle & Shine.