1. Avoid Natural Light!
Nothing fades doll costumes as quickly as natural sunlight. Natural sunlight also fades some vinyl dolls and cloth dolls. Try to avoid storing dolls in rooms with bright natural sunlight, and if you must store dolls in a bright room, at least keep direct sunlight off the dolls.
2. Avoid Fluorescent Light
Even if you knew that bright natural light is bad for you dolls, did you know that fluorescent lighting can also be damaging to dolls, especially to certain vinyl dolls which can turn greenish over time if exposed to close fluorescent lights. Your best lighting bet is incandescent lighting, but not too close to the dolls because of the heat such lights throw.
3. No Smoking!
When someone brings dolls into my store to fix or purchase, I can always immediately tell if a smoker is in the household when the lid of the doll box is removed. Dolls and their costumes absorb the odor of smoke, and the odor is very hard to remove. Many people won't consider buying a doll if it smells of smoke, and the chemicals in smoke are also damaging to dolls and their outfits. So, don't smoke anywhere near your dolls, and don't let others smoke near them, either.
4. Don't Let Dust Accumulate
Dust can yellow costumes and form a hard-to-remove layer of dirt on dolls. If you can't store your dolls in an enclosed cabinet, be sure to remove the dust on a regular basis.
5. Keep Pets Away
Yes, I know you love Fluffy and Fido as much or more than your dolls. But Fluffy and Fido are incompatible with your dolls. Fluffy, your cat, might think doll wigs are perfect mouse-like toys, and Fluffy could well jump-up and knock a doll off a shelf. Fido, of course, might think your prized Barbie is the perfect chew toy. So...if possible, keep your pets and your dolls apart.
6. Keep Bugs Away
You'll also want to keep bugs away from your dolls. Moths can be drawn to wool, and handling your dolls with dirty hands can encourage moths, carpet beetles and many other types of destructive insects. Bugs can eat holes in costumes and cloth dolls, they can infest mohair wigs, and they can bore into wood dolls. Inspect your dolls regularly for bugs.
7. Keep Your Dolls In Closed Cabinets
I know this isn't always possible, but closed cabinets will keep your dolls away from dust, some light, pets and some bugs--in other words, a close cabinet will do more to preserve your dolls than nearly anything else.
8. Avoid Extremes Of Hot and Cold
Extreme temperatures degrade dolls. Heat degrades plastics and can damage composition; very cold temperatures can craze or crack papier mache and composition. Your dolls should be kept at temperatures that you are comfortable in, in a temperature controlled part of your home and not an attic or garage.
9. Keep Dolls Away From Acidic Chemicals
Acids in woods (in cabinets) and cardboard (doll boxes) can damage dolls and costumes. Where possible, use acid-free tissue to wrap dolls placed in boxes, and avoid dolls and costumes having direct contact to varnished woods.
10. Don't Enclose Your Dolls In Air-Tight Plastic
You might be tempted to wrap your dolls in air-tight plastic bags or boxes, but you should avoid this method of storage at all costs. If there is any moisture in the bag or box, mold can form on the dolls. If you must store in plastic, make sure that there is ventilation so that air circulates into the bag or box.
Those are my quick tips; for a more in-depth look at doll restoration, repair and conservation, read my 7-part series: Doll Restoration and Conservation: What You Need To Know