Apply for a visa through the Cuban Interest Section in Washington D.C, if you have a license to travel to Cuba. If you do not have a license, you many obtain a visa through a certified travel agency or at any airport counter outside the U.S. that offers flights to Cuba.
Contact an OFAC (Office of Foreign Assets Control) designated travel agent to book a direct plane departure to Cuba. These are charter flights that depart from Miami and New York. This is an option if you are traveling without a license. Online booking agents such as Hotwire do not offer direct flights to Cuba. Currently there are only 150 American travel agencies allowed to do so. If you have a license, you can fly directly to Cuba from any authorized airport.
Connect through a third country if you do not wish you go through the OFAC. You can fly from the U.S. to Mexico, then from Mexico to Cuba.
Prepare to spend less than $180 a day on lodging, food and transportation. There are travel agencies like Cubalinda.com that are authorized to sell trips to Cuba and can help plan your trip to meet all regulations.