Planting trees, shrubs, and Hedges is a good place to start.
Trim any hedges/trees at this time - it causes minimum disruption to wildlife. If you have wildlife residing in the tree/hedge, try to use non-electric cutters, as not to frighting them off.
Plant pots/containers, you can plant some winter plants in plant pots, or containers, they are protected from any ground frost, but, since this year has been very mild, plants don't seem likely to be effected by any frost
Vegetables to sow in January:
Fruit to sow in January:
(When growing fruits, or vegs, in the winter, you can buy a protective fleece blanket, this protects the fruit and veg from frost.)