Fill a small plastic bowl with water, and squeeze the juice of half a lemon into the water. Set the lemon half in the bowl, and microwave it on high for three minutes. The lemon juice disinfects the microwave and leaves behind a strong citrus smell.
The water creates condensation on the inside of the microwave. To remove stains, rub down the walls and tray inside the microwave with a soft cloth or sponge.
Water alone will remove stains and clean the microwave, but it won't disinfect. A few tablespoons of distilled white vinegar mixed into the bowl of water will both clean and disinfect the microwave.