1. Sunscreen. The single most important thing! I wish I'd been more careful and not insisted on getting a tan every summer during my teens and 20s.
2. Don't overpluck your eyebrows. As you get older, fuller brows will help you look younger.
3. Always wear gloves when cleaning with detergents (dishes, cleaning the bathtub, etc.). I never, ever stick my bare hands in dish-water!