This should be obvious, but many of us get so locked into our plans we forget to take the weather into consideration. One memorable year, an uncle of mine insisted on leaving as scheduled despite a severe storm. The consequence--he was stranded on a shutdown 1-80 in Wyoming. He ultimately made it home a day late--same as if he had waited until the storm was over before leaving. If flying, make sure to check before you leave for the airport and keep in mind that layovers can be problematic because of weather delays.
Tip #2--Be Prepared
Because of weather, traffic, or other delays, you need to be prepared for extra hours on the road (or in the plane). Nothing is more miserable that running out of diapers while hours from landing or wading through slow snowy traffic with hungry little ones. One Christmas, our direct flight was re-routed through a midwest city adding a layover to our trip. We were lucky it only cost us a few hours and nothing more serious (especially since we were flying with a toddler).
Tip #3--Keep Your Sense of Humor
I have posted this tip before, but it is worth repeating (especially for myself). As a big planner, schedule maker, type A personality, I often have to tell myself that someday it will be funny. Someday, it will make a good story. Find your inner peace. From delays, to breakdowns (car or children), to the item you forgot to pack, a sense of humor can help you avoid a lot of problems while traveling this season.