Garments ideally should be washed after each outing, otherwise hang items in a well ventilated room. Garments will maintain the best possible condition if they are washed immediately after being used. By washing the items soon after riding, the onset of bacteria that can deteriorate the fabric is dramatically reduced.
Garments should not be stored in places with high humidity or that lack ventilation. (plastic bag, gym bag, backpacks)
When not in use, garments should not be exposed to direct sunlight for long periods of time.