Expect it to be VERY hot. If it's not, consider yourself lucky. Of course, right now, DC is much hotter than Couples will ever be. You need SPF15, even if you tan easily. (Anything more than SPF15 is a waste of money as you don't get that much more protection . . . just saying). If you tend to burn, limit your time in the sun the first day or so. Seriously. There is plenty of shade . . . take advantage of it.
For first-timers . . . take the resort tour. Do the catamaran tour but, if you plan to jump off the cliff, drink in moderation on the way out. Make reservations at Otaheite at least once. Bring a bit of cash for the beach vendors (local arts & crafts).