Put a towel in clean water, squeeze by hand to let most of water goes out. Then put the towel in microwave oven and heat on full power for around 30 seconds.
The steam which comes from the wet towel could get some of food deposits on the surface loose. After unplug the power plug from socket, open the door of microwave oven and let it cooling down for a while, you can use a piece of cloth to clean the surface.
If the food deposits still exist, please put 1/2 cup of vinegar in a glass then put into microwave oven to heat for 2-3 minutes. Then use a piece of cloth to clean the surface.
Hard detergent, gasoline, abrasive powder or metal brush could not be used to clean any part of the appliance, which may break the surface of microwave oven.