Freshen up the inside of your fridge and keep mildew away by wiping it regularly with vinegar
A dab of orange, lemon or vanilla extract on a small piece of cotton placed inside your fridge will keep it smelling sweet.
Baking soda is good all rounder for removing odours/(odors) so open the box and leave on the middle shelf.
Many smells in your fridge can be dealt with by placing a small tub on the middle shelf with charcoal briquettes inside. They will absorb the odours/(odors).