Cuba's rich cultural tradition and the abundance of highly talented, trained professionals make it a great place to study Spanish. Technological and linguistic glitches, plus general unresponsiveness, make it hard to set up courses before arriving, but you can arrange everything once you get here. In Cuba, things are always better done face to face.
The best official Spanish language courses are available at Cuba's two leading universities: the Universidad de La Habana. It's useful, though not imperative, to book in advance.
Students heading to Cuba should bring a good bilingual dictionary and a basic 'learn Spanish' textbook, as such books are scarce or expensive in Cuba. You might sign up for a two-week course at a university to get your feet wet and then jump into private classes once you've made some contacts.