Plan your itinerary. Pick firm dates for your trip. This will make it much easier to check and compare plane fares, hotel rates and rental car costs and to make reservations for your visit. If you are not staying with family or friends, choose the exact city or town where you will stay. Include special sights or activities which you do not want to miss. Prepare a travel budget based on what you can afford to spend. Even a rough vacation plan will serve you well as you work to firm up the details of your trip.
As soon as your plans are in place, book your flight and reserve your hotel room and rental car. The earlier you do this, the better, as flights, cars and accommodations are more limited the closer you get to the holiday. If you do not have a passport, apply for one immediately. Normal processing time for passport applications is four to six weeks. Expedited service is available for an additional fee and processing time runs two to three weeks.
When packing for Christmas in Greece, don't make the mistake of thinking you will need parkas and snow boots. The average temperature in Greece in December is around 59 degrees, so slacks, thin sweaters and maybe a light-to-medium jacket should be sufficient. If you are taking holiday gifts along, consider shipping them separately rather than paying the airline rates for extra baggage.
Don't worry about obtaining a visa. U.S. citizens are able to enter Greece without a visa under the Schengen Agreement for periods of 90 days or less.
Consider learning Greek. While you can probably function quite well with English in the metropolitan areas, it's always fun to be able to converse in the native language. Consider a group or independent study of Greek or pick up a phrase book to take along in case you find yourself in need of it.