Check for Problems in the Garden
Walk around the yard to see if any perennials have become pushed out of the ground by periods of freezing and thawing. If so, push them back into the ground and cover loosely with evergreen branches or tree leaves. Check young trees to make sure rodent guards are in place or add them if not yet done so. Also, wrap the trunks of young trees with white tree wrap. Re-apply or apply anti-dessicant spray to broad-leaved evergreens.
Consider Fruit Plants
If you add nothing else to your garden this year, please make it be fruit plants. No other addition will bring such benefits to you. Top of the list should be blueberries, because they are on everybody's list as being a nutritional powerhouse. The plants are long-lived and a beautiful addition to the landscape. Raspberries need only minimal care; research has shown 'Caroline', an everbearing red variety, to have the highest nutrition. Blackberry 'Triple Crown' will inundate you with fruit.
Work on Vegetable Garden Planning
It's time to settle in and figure out what you want in this year's food garden. Buy seeds and plants early for the best selection. You probably have favorite vegetables and varieties thereof, but experiment with adding some additional ones. Growing your own food does save money and makes you healthier as well.
Start Looking for Little Bulbs
Snowdrops (Galanthus nivalis and relatives) are among the earliest of the flowering bulbs to push through the frozen ground and snow to bear their green-tipped flower droplets. Not far behind will be the snow crocus, eremus, scilla, iris, and others. Most of these are small plants with small flowers, but the joy and hope they bring in the depths of winter is enormous. If you have these in your garden, go out and say hello to them and thank them. If you haven't planted them, then visit a botanical garden to see what you're missing.
Prune Trees and Shrubs
Anytime the temperatures are above 20 degrees F is a good time to do winter pruning of trees and shrubs, both those that are ornamental as well as those that produce edible fruits. Also remove suckers from the base of trees. Candidates for removal include branches with narrow crotch angles, which are more likely to break in wind and ice storms, and those branches that cross. Branches should be cut flush to the branch collar, which is the natural swelling that occurs where a branch connects to the trunk.