1) Slather on the sun screen. Applying a generous amount at lease 30 minutes before going outside is best. Reapply every two hours especially if you're playing beach volleyball or swimming. You have a lot of options for sunscreens, but be it gel, lotion, spray or stick make sure it has an SPF factor of at least 15.
2) Be aware that not all cover ups are created equal. Clothing can offer great skin protection, but not all clothing offers the same protection. A white T-shirt has an SPF factor of only 7, while even a dark green shirt of the same fabric is SPF 10. Laundry additives such as Sun Guard can be added together with clothes in the wash to substantially increase their SPF protection.
3) Wear a hat and sunglasses. A broad brimmed hat that expands 3 to 4 inches around the entire head is best. Baseball caps give great coverage to the face, but fail to protect the neck and shoulders. It's easy to forget the delicate skin around the eyes and that the eyes themselves need protection too. Wearing UV protective sunglasses can also help prevent glaucoma later in life.
4) Avoid sun exposure during the hottest part of the day. Do you really want to bake? That's a great time to have a lunch or lemonade break and head indoors for an hour or so.
5) See a dermatologist once a year - Just before bathing suit season is a good time to go. You can get prevention tips; find out your risk factors for skin cancer, and determine whether you need to do monthly self-exams.