Store your shoes in dry places well away from moisture. Moisture is bad because it promotes bacterial growth and causes the material of your shoes to disintegrate easily when you finally wear them after some time.
Use silica pouches or gels to keep them moisture-free. In case you don’t have silica gel, you can stuff your shoes with newspapers and change them after a week or so, thereby protecting your beloved soles from moisture. The newspaper stuffing will help to absorb the excess moisture in your shoes. Remember that keeping them dry is always the key.