A healthy diet and lifestyle is a great start. Keeping a fresh youthful appearance begins inside with our attitudes and personal habits. As Jonaj mentioned, steer away from the caffeine, give up smoking and minimise sun exposure. Avoiding alcohol is also important and drinking plenty of purified water to keep your body hydrated is strongly recommended. Many people swear that following a vegetarian or vegan diet works wonders, and sticking to organic foods, if it's possible. I also take a teaspoon of a German silicon supplement called Silicea which supposedly minimises the appearance of fine lines, and is beneficial for nails, teeth and hair.
Externally, I'll only use organic skin care products and especially like using pure oils such as rose hip, jojoba or avocado oils. They're quite affordable and a small bottle lasts me for ages. In hot climates, always wear a hat and a good quality organic sunscreen.
Keeping fit (but not overdoing it) is also important as it keeps you healthy and positive. Yoga is especially good, and many people I know who do it regularly look years younger than their chronological age.
Finally, real beauty is not about how many or few lines and wrinkles we have. It goes beyond the body. Some of the most beautiful, inspiring people I know are the most wrinkly!