Use a sunscreen with a Sun Protection Factor (SPF) of at least 15.
Some types are waterproof, but even so, you should reapply the sunscreen every two hours
Use sunscreen on cloudy days, too.
It may be slightly uncomfortable in the heat, but you should wear a long-sleeved shirt and long pants.
Also put on a hat with a large brim and sunglasses.
If you have a choice, stay in the shade. Beach umbrellas will protect you from some of the sun exposure. They are actually very comfortable on sunny days.
Remember that children’s skin is even more sensitive that yours. They can start wearing sunscreen by the time they are six months old. Even so, minimize their exposure.
Avoid tanning parlors.
The sun is strongest between 10 a.m. and 4 p.m. Hit the beach early, use the main part of the day for other activities, then go back later in the afternoon.