You should start by unplugging the refrigerator. Next, pull out any shelves or drawers that can be removed, and give them a soapy bath in the kitchen sink. Before you put those fixtures back in, clean every surface inside the refrigerator with a mix of warm water and baking soda. (You'll find different "recipes" online, but try two tablespoons for every gallon of water.) Remember to get into the nooks and crannies; ie. the shelf supports.
After you have cleaned, you'll need to wipe everything down with a dry cloth and let the refrigerator air-dry.