Just back from: Curaçao
What's the #1 tip you'd give a friend who wanted to go? The Dutch were good administrators and flawed colonialists, and the island lacks many of the macro problems that can make the Caribbean a drag. The charming, pastel-painted colonial capital city of Willemstad is a UNESCO World Heritage Site. Also, almost no bugs.
What did you do? A whole lot of nothing, punctuated by snorkeling, scuba, and circumnavigating the entire island, which can be traversed in about three hours.