WARM ON TOP
A good hat is crucial. It should protect not only the head, but also the ears and neck.
Gloves should give good protection to the hands while allowing adequate freedom of movement.
Wool is by far the superior material when it comes to finding warm socks, because it continues to have a warming effect, even when moist.
Choose footwear that is somewhat larger than you would normally use; so you can fit extra socks and/or insoles. Also, this will keep your feet warm for longer. Also, remember that you can retain heat by changing socks and mittens a couple of times throughout the day.
The purpose of the outer shell is to provide protection against water and wind in combination with the outer layers. The material should breathe and allow full freedom of movement. Additional clothing is used at very low temperatures; a down jacket or a thick fleece or wool sweater works as an effective additional garment to keep warm.
The layer nearest to the body needs to transport moisture away. Choose thermals in a synthetic material, wool or a wool mix. Fleece, preferably windproof, makes an excellent midlayer.