1. Limit light exposure.
2. If you feel comfortable, your treasures will be comfortable.
3. Avoid extremes of temperature and humidity.
4. Create micro-climates and use protective covers.
5. Inspect your treasures regularly and tend to problems as they arise.
Light and temperature are the two biggest culprits when it comes to deterioration in most things. So, limit light exposure and don't put things in direct sunlight. If you feel comfortable, your treasures will be comfortable. You probably wouldn't be comfortable living in a damp basement or an attic in the middle of July and neither would your family treasures. Maintain a moderate temperature, around 72 degrees with 50 percent relative humidity. Create a safe haven for your stuff by using chemically stable boxes, matting and framing with acid free materials, and dust covers. Periodically check your things fo make sure they are in good order. It doesn't cost anything to check to make sure things are properly stored, but if you neglect things and they become damaged it can cost you thousands of dollars to repair.
Thanks to the Institute of Museum and Library Services.