Clothing around your neck should be adjustable or removable so you can vent body heat and perspiration. Choose jackets with zip collars, zip turtlenecks, neck gaiters and silk scarves. For very cold weather, choose insulated pants specially designed for riding. If you wear jeans or breeches, have a roomy pair for winter and use lightweight silk or polyester drawers under them. Try a silk underlayer, a down middle layer, and a nylon waterproof breathable shell.
Some jackets perform the functions of the middle and outer layers.
During temperatures in the thirties and forties, when a jacket is not be necessary, a good combination is a silk turtleneck, wool sweater, and tightly woven riding vest. Choose outer garments that unzip or unsnap from both the top and the bottom and have rear gussets which unsnap to cover the cantle. Be sure your riding jacket allows freedom of movement in the shoulder and arm area.