Toaster ovens, waffle makers, panini machines, blenders, mixers and other small appliances usually get cleaned right after they are used. Some of these small appliances make have difficult to reach parts that can be taken apart to be even more thoroughly cleaned. Periodically check your small appliances and do a deep clean to all the parts as necessary.
Creating a mixture of white vinegar and water is great for cleaning most appliances. You can use it to wipe down an appliance, or you can use it run through an appliance like a coffee maker, juicer, or mixer. After running through the mixture of vinegar and water mixture, rinse the appliance with just water.
Here is a video from Good Housekeeping.