Brass monkeys and Backache.

It's time to look around the site and see who's busiest.
Is it the gardener with the plot full of overwintering crops or the one with the bare soil?
Surprisingly it's the latter.Now is the perfect time to dig over the bare patches on the plot, the empty beds so the frost can get to the lumps of solid clay and break them down. It is good housekeeping to expose the soil borne pests too, when the frost can nip them and the hungry bird population can feast away on those grubs and crawling nuisances.
It is the constant freeze, thaw, freeze thaw cycle that breaks the clay blocks down to a friable, crumbly texture in time for spring sowing.
Digging is a skill in itself, to be learnt slowly and carefully.Going at it like a bull at a gate will result at best in a stiff body and at worst, permanent back damage. Sloppy digging, just turning over the surface, will do the structure very little good and will provide handy hiding places for the diseases and viruses, pests and such to stay warm and survive until next season.
Take your time, set yourself realistic goals and keep warm. Before you start, warm up, as you should with any exercise. Digging is one the cheapest and most beneficial forms of outdoor exercise you can partake in in the winter.
Mark out an area you think you can manage, halve it and expect to struggle to finish that much on your first attempt.
If you have particularly weedy or un-worked soil, keep a barrow or bucket nearby to toss the roots of any perennial weeds into, trying to avoid breaking up any roots as most weeds can regenerate from the smallest piece. Take regular breaks to straighten up, have a warm drink and review your progress. Don't forget to cool down properly after work as it means the difference between a sense of achievement and a stiff back. Usually, the time it takes to clean and oil your tools before storing them away will be enough to allow your muscles to ease back to normal. If you have a large area to work, take a quick picture before you start the project and take a progress picture every time you stop and pack up. That way, you can see how much you have done and how much nearer you are to the finish. A little self encouragement is always useful.
Just remember, no matter how big a plot you have, it's always best tackled one bite at a time.
This is one job in which there is no prize for finishing first.