Underneath and behind appliances that sit on the counter AND on the floor- I used to forget to pull out appliances that were on the counter top in the kitchen when I cleaned. That was until I dropped something behind the microwave, pulled it out and saw all the dirt and dust and crumbs. But its important to do. Check under the coffee maker, toaster, etc. I know it’s a pain to pull larger appliances like that out, but be sure to clean under there every once in awhile.