In Cuban culture, Cubans are generally friendly and helpful people. Keep in mind that they make about US$15 a month; if they can help you, they probably will, but they may expect you to return the favour. If you are invited into a Cuban's home for supper, take the invitation.
You will really be treated like a guest of honour. It is a great way to get a feel for the culture. Of course, ordinary Cubans are not permitted to host this type of event, but it goes on as a matter of course.
One way to help local Cubans is by staying in Casas particulares and eating in paladares. While free enterprise is usually banned, several years ago the government began selling expensive licenses to individuals wishing to open up rooms for rent in their houses, or set up a few tables on their porch and cook out of their kitchens.
Not only are the licenses very expensive but the fees must be paid monthly regardless of income, leaving those less fortunate the possibility of actually losing money. Not only is it more interesting to stay with locals and eat in their homes, but you're also actually directly benefiting them in one of the few ways possible.
Do not push Cubans into a discussion of political issues, as this could have serious repercussions on you and the person to whom you are talking.
Traditionally Cuba is Catholic, but the government has often cracked down on demonstrations of faith. Recently, however, it is less frowned upon since Pope John Paul II's visit, and there are more important issues to deal with.
Other religions in Cuba are hybrid religions, mixing elements of Catholicism with others of traditional African religions. The most common one is called "Santería" and their priests can be recognised by the full white regalia with bead necklaces that they wear.
Women going through the process to become priests are not allowed (amongst other things) to touch other people, so if your casa owner is distant and dressed all in white, do not be too surprised.
There are many museums in Cuba (especially in the Southern cities like Santiago de Cuba) which depict the history and traditions of Santería.