SUN SENSE
Simply put - it's all about common sense. Baking for hours on end under a hot tropical sun is not a good idea for anyone. But if you enjoy the sun and insist on going out in it, the best advice is to know your limitations. The rules don't change because you're on vacation.
The time of year, cloud cover, and location are all factors that will effect the UV index, (This is the amount of radiation you will absorb depending on the amount of time you're exposed.) but where ever you are you should be protected. Start with a sunscreen with SPF rating of 25 or greater, avoid the midday hours when it's hottest, wear a hat, and drink plenty of water.
The current thought, I should add however, is that while some screens slow reddening they do not stop the absorption of UV radiation. The accumulation of this over the years may possibly induce the onset of skin disorders, such as melanoma.
So, again, the rule of thumb is to know your limitations and follow your good sense.
Do that and you'll be able to enjoy the sun and still have a good trip.