For water-resistant or water-proof gear, I apply a DWR (durable water repellent) finish via aerosol spray about once or twice a year to gear that absolutely needs it (rain shell, rain pants, hiking pants, boots). I try to do this as infrequently as possible, or before a winter trips where failure of the membrane would be very unpleasant or dangerous.
For other clothes - base layers, fleece, etc - I wash them as little as possible or only when they are visibly dirty (or stink to high hell). I hand wash or do gentle cycle in a machine and almost always line dry. For more durable items (e.g. GoreTex boots), I scrub them with a soft bristle brush under warm water.
Storage is ideally hanging in a cool, dry place with no direct sunlight, but this isn't always possible. I live in a city, where closet space is at a premium, but if you live in a house and also don't want to clutter up your closet, I would say a basement is better than an attic. Regular use will be far more degrading to a membrane than folding, and by the time the membrane is failing you will probably be onto the next big thing, whether due to fashion or technology. That said, there are some who say that crumpling is better than folding because you aren't always stressing the same area of the fabric/membrane, but these people are probably also just slobs.
