For the most complete sun protection:

Use sunscreen. Use a broad-spectrum sunscreen with an SPF of at least 15. When you're outdoors, reapply sunscreen every two hours — or more often if you're swimming or perspiring.
Seek shade. Avoid the sun between 10 a.m. and 4 p.m., when the sun's rays are strongest.
Wear protective clothing. Cover your skin with tightly woven long-sleeved shirts, long pants and wide-brimmed hats. Also consider laundry additives, which give clothing an additional layer of ultraviolet protection for a certain number of washings, or special sun-protective clothing — which is specifically designed to block ultraviolet rays.