Basic Cleaning
Wipe your microwave with a mild detergent and water. Rinse well and wipe it dry with a paper towel. Don't forget around the edge of the door. For a more thorough cleaning, unplug the microwave and use a vacuum to remove food from crevices inside the microwave. Vacuum around the fan and outside of the microwave, too.
Steam Cleaning
Steam cleaning, when done right, can help loosen particles stuck to your microwave and remove any odors clinging in your microwave's vent. Measure 1 cup water into a large glass or bowl and add one of the following: 1 to 2 tbsp. baking soda, 1/2 lemon, 1/3-cup lemon juice or 1-cup vinegar. Place it in the microwave on high for three minutes. Wait five minutes before opening the microwave. Wipe off the inside of the microwave with a clean sponge.
Odor Removal
If you've tried lemon juice, vinegar and baking soda and the odor still lingers, there are a couple other things you can do to help get rid of the odor. Place 1 tbsp. vanilla extract or 2 tbsp. coffee grounds into a coffee cup half-filled with water. Microwave the mixture on high until the water boils or about three minutes. Stop the microwave and let the cup sit for five minutes. Crumbling newspaper and stuffing it into the microwave overnight can also help absorb odors. Remove the newspaper before running the microwave.
Prevention
Prevent future odors by wiping down your microwave after you use it, especially if you cook foods with strong odors like fish or broccoli. Cover dishes with wax paper, paper towels or some other cover to cut down on spatters. If your microwave does not have a glass plate or shelf on the bottom, place a plate or paper towel under the food as well.