Once the seed catalogues start showing up in the mail, I get the bug to start planning for next year's garden tasks. What do you do during the winter to prepare next year's garden??
With the ground as hard as a brick, there isn't much to do in a garden right now in New Hampshire. Unless you own a backhoe you aren't going to break ground. Even in a greenhouse things are moving very slow unless you use a lot of supplemental heating and lighting. Things just sort of shutdown around here during December and January, but towards the middle of February there are signs of hope with lengthening days and the long stretches of cold weather behind us. I am considering the use of "Quick Hoops" to extend the growing season, and they could make March and April productive.
February is a good time for pruning fruit trees in that the tree is still dormant, and you probably won't freeze to death while doing it.
So, the short to your question is "not much", at least until February.