We frequently get told we should be drinking more water and I am one of the biggest culprits. Skin needs moisture to stay flexible so even mild dehydration will cause your skin to look dry, tired and slightly grey.
Drink six to eight glasses of water a day - all fluids count towards your daily allowance, but water is the best.
If you work in an office, keep a large bottle of water on your desk to remind you to drink. Herbal, caffeine-free teas are good too.
Of course, it's common knowledge but really try to avoid smoking and excessive alcohol consumption as both can age the skin.