1. It's been said many times, many ways: Plan ahead! Thinking and planning ahead, even a year in advance, is not a bad idea when you're talking about travel during a holiday season. In the case of many popular destinations, it might in fact be necessary to start planning that far in advance. So be sure to give yourself plenty of time to decide on a location, make a reservation, save money as needed, exchange currency online or ahead of time for international trips and take care of the other details that definitely can't be "last minute." The more you do in advance, the less stress will accompany your actual travel.

2. Get everyone involved together; make lists, check twice. Are you planning a vacation for yourself, for you and another person, for you and your immediate family, or for a big group of people? Maybe you're not even sure yet. One thing to consider right off the bat when planning a Christmas vacation is "Who is coming with me?" If it's just you and one other person, your task will be simple. But if you are planning on a large group vacation, a lot of coordination is needed. So, get together with those involved in the trip and plan the basics: like when you're all available, what a workable budget would be for all involved, and, obviously and most importantly, where you want to travel! This kind of "group planning session" is important in making sure everyone has a good time on the trip.
Of course, if you find you can't plan sanely with your intended travel companions, that may be an indication you won't have such a great time actually traveling with them either. That's definitely something you want to "know before you go."

3. Check for holiday specials, group packages, blackout conflicts, and a partridge in a pear tree (optional). Either using a travel agent, an online services (like Priceline or Orbitz) or by directly contacting the place you're staying or visiting, check for special holiday packages that companies may offer in anticipation of big holiday crowds. Also, you may want to see if traveling just before or just after Christmas can save you a lot of money or provide you with better options on accommodations.
If you're traveling with a large family or group, look for discounts that might apply. Also, be sure that special discounts you had planned on using - like credit card airline miles or a AAA discount- are usable during the Christmas season. Unfortunately, some programs have blackouts during this busy time of year. Another thing to "know before you go."

4. Don't just dream of a white Christmas, set up a "travel account" and save for it. The holidays can be expensive even when you're staying home. A Christmas vacation brings all the usual travel expenses. In the beginning stages of planning your trip, you and your companions will have established a budget, but the money for that budget may need to be accrued over time. If possible, set up a formal or informal savings account for your travel expenses. This will allow you to put away a little over time - an option most people find preferable to maxing out credit cards or coming up short at the last minute. If you like, also save for presents and other extras you may want to splurge on when you're on your big trip.

5. Be home for Christmas, if only in your hotel room. Many resorts and popular travel destinations go "all out" decorating for Christmas. It's unlikely you will go some place where the time of year isn't at least somewhat obvious. But to make the holiday more personal, don't hesitate to bring a few Christmas things from home to brighten up your hotel room. For instance, maybe you and your kids have special ornaments or stockings you can bring with you and hang, or maybe you have a special Christmas music box or even some mini-lights.
I don't suggest bringing your own full-sized evergreen with you, but taking along some personal touches can keep you in touch with family traditions. Of course, what you do about bringing presents is up to you. Some people may prefer to open gifts before or after hitting the road for the sake of convenience. Other people find a way to take the presents along so they're on the scene Christmas morning.

6. Check out local holiday events (I hear the Whos down in Whoville throw a pretty good bash...). If you're going away for a holiday to some place with a culture different than your own, take some time to experience how they celebrate Christmas. Watching, or even taking part in, a special cultural celebration can end up being one of the most special parts of your trip. If you're going some place where the cultural traditions are much like your own, check out what events they have planned like musical events, shows or religious services. Many of these things may be included in your travel package; others you may need to track down on your own.

7. Don't expect perfection. Sorry, I'm tapped out for songs. Christmas is a season that is often filled with high expectations. Often, having expectations that are too high simply causes stress and disappointment. So think of your Christmas vacation as a time for enjoyment, not a time to make sure everything goes 100% according to plan. Many travelers can attest to the fact that the unplanned part of a vacation is sometimes the best part.
It's true, a Christmas vacation may take time and effort to plan, but a great Christmas vacation will leave everyone involved with equally great memories and may have them asking right away: "So, where are we going next year?"