It is recommended that to extend the life of your mask that you keep in mind that sunlight, fluorescent light, ozone, and most oils are harmful to latex rubber. So when not in use it is best to powder the inside lightly with unscented talc, stuff with tissue paper to reduce wrinkles and store in a plastic bag or box , away from excessive heat and light.
To protect against dirt it is best to apply a thick coat of silicone spray or Armor-All to the surface, but it is also possible to wash your mask with a mild detergent and water then blow dry.
If your mask has hair you may keep it groomed by gently brushing it layer by layer with a dog brush. You can expect to pull some hair loose with every brushing, but if you brush gently the amount of hair loss with be minimized.