Ultraviolet light, UVA and UVB from the sun causes 90% of premature aging so sunscreen is probably the most important thing you could do.
Moisturize your skin and be careful of supposed anti-wrinkle creams because a lot of the time they contain ingridients that make your skin even more sensitive to the sun leaving yourself more open to sun damage. Research any anti-wrinkle/aging product ingridients before using them. Most of the time these products actually just plump up your skin to temporarily smooth out the skin.
As for diet:
Yes to water, fruits, vegetables, fish.
No to recreational drugs and too much alcohol.