It amazed me that so many people did not expect the heat and humidity on many of the islands while other islands have cool ocean breezes that made 80 degrees feel quite comfortable.  Do your research.  Be sure to check if your tour bus or excursion is air conditioned if it is a problem for you.

The unhappy cruisers were the ones who did not dress adequately for each port accordingly and were especially unprepared for the frequent rain that lasts about 3 minutes.  Poor choice of shoes was the biggest mistake most people made.  Cheap rubber flip flops do not work well on the many uneven concrete or cobble stone paths.  "Hiking boots" are way too hot for island walking.  Leave the frilly dress sandals on the ship.  

Hats that tie under the chin or baseball caps are about the only type that stay on.  It is generally very windy when you disembark especially if another ship is in port and you are walking between ships on the dock.

Gotta love the ones that say I never burn and don't use sunscreen who return to the ship with the sunburn of a lifetime!

And last but not least - the islanders.  So many people express fear and feel "unsafe" when there is really no valid reason in that particular port to feel that way.  They equate poverty with crime and confuse island life as threatening for some reason.  Tourists are the livelihood for many islands and increased security near ports is common.   Don't stray off the tourist routes and you will do just fine.