Winter practices, internal and external alike, mind the Kidneys. This is the season when Water is born, and like any newborn, it is both at its strongest (all the potentials are there, ready to start unfolding, nothing has been used up yet) and its most vulnerable.
One of the things to be mindful of at this time is that it is the season of many "pernicious influences," and protect the Kidneys with utmost care. Cold penetrates and moves down in the body, accumulating in the kidneys, lower back, abdomen, legs. Don't let it accumulate. Protect your lower body and especially the kidneys area with adequate clothing, don't get chilled there. Don't eat or drink anything cold, and make a habit (if you haven't already) of eating soups throughout the season, preferably every day. This is more important than herbal elixirs and tonics, but if you want to use these, the warming, yang formulas are best taken during this period, plus those that replenish Protective qi.
Make a habit of massaging your kidneys for a minute or two every time you feel cold or low on energy. Do not indulge in any excessive activities, but do not give in to lethargy -- "slow and steady" is the spirit of the season, "even and persevering without exertion" is the mood to cultivate to match its energies.
May I add some uncommon things?
Drink something warm before and after practise
to relax the diaphragm, especially after one came
from the cold and want to practise.
If you want warm up your Lungs which is attacked by the
Cold by breathing the air one hold the warm water
long in mouth while one breath slowly
(works better with rice.)
Ever try to breath through rice
(just dont breath the rice in)?
(The rice pictogramm in one of the "Qi"
in Chinese Character - actually eight direction....)
This is awesome.(Dont breath into the rice,
you dont want cool it)
Also if you want sweat out cold that is accumulated
then it is good to use "spring onion" in water
to move it out adding "ginger" it opens the pores.
If the coldness cause stucking of toxins
because of closed pores then use apple vinegar
-some drops- in warm water to cause it to be
Else Water Path like exercises are enhanced in
this time when a downward flow is needed.
Also its good time to meditate.