12. Feed your face with vitamin C.
"I put vitamin-C products in the hedge-your-bets category," says Rodan, who uses one under her sunscreen to combat the free radicals produced by whatever ultraviolet light that gets through. A study published in the Swedish dermatology journal Acta Dermato-Venereologica showed that when used with a sunscreen, vitamin C provided added protection against ultraviolet B (sunburn-causing) and ultraviolet A (wrinkle-causing) rays. Rodan's picks: serums that contain L-ascorbic acid, the form of vitamin C shown in studies to be more readily absorbed by the skin's cells. Products that contain L-ascorbic acid include Cellex-C High-Potency Serum ($90; 800-CELLEX-C), SkinCeuticals Topical Vitamin C High Potency Serum ($60; skinceuticals.com) and Citrix Cream L-Ascorbic Acid 10% ($50; clavin.com).
13. Experiment with caution.
"I spend several thousand dollars a year trying new products, but I don't try them all at once," says Lisa Airan, M.D., clinical instructor of dermatology at Mt. Sinai Hospital in New York City, who's in her early 30s. Airan routinely sees patients with dermal disasters -- like breakouts and red, raw skin -- caused by overuse of products. Those particularly susceptible: women with acne or sensitive skin, who should only use products formulated for their skin type unless otherwise directed by their dermatologist.