The key is: Keeping your hands, feet and neck warm. Don't let cold air down your back either. Wear layers....I found that wearing my leathers with insulated rain gear overtop works well to block the wind. If you block the wind, the core stays warm. Also, I wear one of them snowmobile neck thingys.....IT WORKS AWESOME. Typical cold weather gloves and good socks. Toe warmers would be in order for a long ride. I'm waiting to catch a snowbile one piece suit on clearance....that would solve all the cold weather problems. Buy it large enough to fit over your leather riding gear.......That would be Heaven!
Good luck
DD