Visiting Cuba will be easier when direct flights begin later this year. Keep an eye on Frontier Airlines, which has applied to fly nonstop to Havana from Denver International Airport. When I visited the island with my girlfriend last November, we had to fly to Mexico and buy separate tickets to Havana. Because of the embargo, Aeromexico refused to speak English while booking our flight to Cuba, forcing a transaction in Spanish via their Mexico City offices. (They also later canceled our seats without notice, trying to shake us down for twice the price the day our flight left Cancun.)
A friend who'd recently visited Cuba wisely advised us to carry only euros, as debit and credit cards rarely, if at all, would be processed. (U.S. dollars were hit with an extra 10-percent conversion fee, making them a poor choice.) We carried a Lonely Planet guide printed in October 2015, but even it acknowledges change is happening so rapidly on the island that some info would soon be out-of-date.
A couple years of high-school Spanish helped immensely, as most Cubans speak little to no English. Download a free Spanish-English dictionary app that will function sans wifi — 'cuz good luck finding any outside pricey government-run hotels or public plazas. We had zero phone or data services.
Book overnight stays in casa particulares (residences). They're widely available and discernible by doorway signs with a blue symbol and the words "arrendador divisa." Hosting families pay the government a hefty monthly fee to operate, and they faithfully record your passport info. So if you'd like more of your money to go directly into the pockets of Cuban citizens, buy breakfast and dinner from your hosts. Each meal will generally run you $5 per person, plus the quality is equal to, if not better than, most restaurant meals.
We focused nine days on three locales: Havana (museums, architecture, city life), Viñales (countryside, tobacco farms, slow pace) and Trinidad (gorgeously preserved, coastal, colonial). We used buses and group taxis, which weren't always easy to organize.
Other critical info is covered by guidebooks, but be prepared to figure out a lot on your feet. If you aren't the adventurous type, maybe wait to go until you hear of a Starbucks opening.
The Cubans we met were incredibly gracious and welcoming, eager to help out and excited to host Americans. We felt safe touring Havana, even late at night, down streets that in many other cities would say "walk me if you like to be robbed." But we never felt threatened. Be as vigilant as you'd be anywhere, but don't stress.
Finally, be prepared for propaganda, the charm of a place largely frozen in time, and great beauty. Oh, and fine rum and cigars, of course.