First, the "what," before the "how much": Tip in convertible pesos only. With CUC, you give that person access to purchase otherwise scarce goods. Some visitors "tip" in consumer goods, leaving behind aspirin, vitamins, school supplies, or pens for the hotel maid or a Spanish-English dictionary for a tour guide. That is fine, but always consider such items additional gifts. Cash provides the best help for these struggling, hard-working people.
In hotel restaurants with buffet-style meals, you can tip the waitstaff CUC$2–CUC$3, depending on the extent of service and the number of people in your party. Elsewhere, tip waiters and waitresses 10%–15% of the check. Tip hotel maids CUC$1 a day and porters CUC$1a bag. Tour guides should get CUC$5 per person. Tips should also be given to museum docents, taxi drivers, and anyone who keeps an eye on your rental car for you. For most of these people, CUC$1 is usually enough; if your cab fare comes to more than CUC$10, tip the driver 10%–15% of the total. Cubans who work in the service industry rely heavily on tips to merely subsist; therefore, you may feel better if you err on the generous side. You should also consider tipping people you wouldn't elsewhere, such as receptionists, rental-car agents, public-relations people, travel agents—all of whom earn CUC$10–CUC$15 a month—and hotel doctors, who earns less than CUC$30.