Don't worry about mileage. Set a time and adjust the intensity of your workout. Shorten your stride and keep your feet closer to the ground. This will improve your footing on icy surfaces to decrease your bounce and maintain control. Choose to run over snow rather than ice.
Snow has more traction.
If possible, run into the wind on the first leg of your run. At the end of your run, you're typically going slower, causing your body temperature to drop. With the wind at your back, not only will you have less cold air hitting your face, but the wind will give you a nice boost to coast home. In extreme temperatures, cover all exposed skin with petroleum jelly. Have your running partner check your face from time to time for white spots caused by frostbite.