Since January 2008, new tourism cards no longer ask for proof of three nights’ pre-booked accommodation upon arrival; however, it’s wise to have pre-booked rooms or, at least, the address of a hotel or casa particular (private room rental) in mind in case you’re questioned.
Christmas and New Year’s are particularly busy, as are major festivals. Book well ahead; call direct, send a fax or email, or have a tour operator abroad make your reservation (the latter are sometimes cheaper thanks to wholesalers’ discounts). Insist on written confirmation and take copies with you, as Cuban hotels are notorious for not honoring reservations. Pay in advance for all nights you intend to stay; otherwise you might be asked to check out to make room for someone else.
Charter package tours with airfare and hotel included may offer the cheapest rates, although the less notable hotels are often used.