If you’re familiar with DIY cleaning, then you won’t be surprised by the secret ingredient for cleaning coffee mugs, baking soda. It would seem that the magic of baking soda knows no bounds! Sprinkle a little bit of baking soda directly into the mug and scrub with a damp cloth. The abrasiveness and cleaning power of the baking soda should wipe away the stains without much effort. Rinse thoroughly.