I find if I’m far away with my telephoto lens, I say nothing, but if I’m up close I would ask them if they mine.( most if not all are just fine) Just like you would anywhere else in the world.
Do not take any pictures of any military subject at all. Do not take pictures of a jail, prison or the police. I would not even take a picture of the security at the resort.
Everything else is fair game.
If you would like a site that will be able to give you a lot more advise try here:
http://www.tripadvisor.com/ShowForum-g1 ... -Cuba.html
Hope This helps!