By far the biggest enemy to a motorcyclist on the road in cold weather is the wind. It will literally chill you to the bone, and at 60 mph (96 km/h) or more, it hits you like a bucket of ice water if you aren't prepared. One of the best ways to protect yourself from the wind is to avoid it as much as possible. An easy way of doing that is to install a windshield on your bike.
A windshield on your bike functions the same as a Viking's shield used against the mighty ax; it deflects the majority of the blow and keeps you safe at the same time. With a windshield on your bike, most of the cold air you're rushing through at 60 mph will be simply diverted around you instead of hitting you straight on. The upside is that you'll avoid the worst of the wind and will stay warmer as a result.
A windshield is an easy accessory to install. You can do it yourself or take it to any major dealership. Once it's in place, you'll find that the difference, in terms of how much wind is actually diverted, is huge.