Just got back from a week there. Go snorkeling and island hopping. Several of the companies there will take you out for a decent price.
Check out the Tipsy Tuna and Barefoot bar that are right on the beach at the southern end of the peninsula.
A lot of amazing places to eat and food prices aren't bad. Some of our favorites were Rumfish Y Vino, 1981, Maya Beach Bistro and Hobbs barge which has craft beers and good food.
Don't really have any dont's except avoid Seine Bright at night if you're on a golf cart. It can be a little sketchy after dark. And be prepared for the heat, pretty much everywhere but your room and few shops don't have any ac and if you aren't on the beach side with the breeze the humidity is killer.