Use Leftover Evergreen Boughs
If you have greens leftover from cutting branches off the Christmas tree, or from decorating, use them to help insulate roses and perennials. Even if there's a covering of snow, lay the boughs on top of the plants in as thick a layer as possible. They won't compact like a mulch of leaves will.
Keep Off the Grass
If Mother Nature hasn't blessed you with snow cover on your lawn, don't walk on the frozen grass because you'll break grass blades and may cause dieback in your lawn that will show up next spring. Put up flagging or stakes in sensitive areas to keep visitors on the path.
Plant an Indoor Herb Garden
The outdoor gardening season may be over, but indoors you can grow many herbs. Sow seeds of parsley, oregano, sage, chives, and dwarf basil in clay pots. Once they germinate, place them under grow lights and water and fertilize (with a half-strength solution) only when very dry. You'll be rewarded with fresh herbs for your winter cooking.
Peruse Gardening Books and Magazines
If you have some time off during the holidays to relax, settle in with some old gardening magazines and books to learn something new or research a question that nagged at you last planting season when you didn't have a moment to spare. Or visit a bookstore to see what's new. If you glean some new ideas for next year's garden, you can add them to your list of New Year's Resolutions.
Keep Holiday Plants in Cool Temperatures
You'll get longer-lasting blooms if you keep paper white narcissus, cyclamen, amaryllis, hydrangeas, and other blooming holiday plants in the coolest spots. To really slow down the blooming, move plants into a cool basement; to speed things up -- in the case of stubbornly slow bulbs -- move them into a sunny window.