Put on the Right Clothes
Layers that you can shed are essential. Start with a moisture-wicking base, a mid layer for insulation, and an outer shell for blocking wind. A vest (like The North Face's Animagi, $120 @ thenorthface.com) keeps in body heat without sacrificing mobility.
Protect Your Extremities
Most of your body heat is lost through your head and hands, so gloves and hat are a must. Make sure whatever you pick is compressible, so you can shove 'em into a pocket or your waistband if you get too hot. For your feet, choose wool running socks, like SmartWool PhD Running socks ($16 @ smartwool.com). They're thin, breathable, and warm, even when wet.
Be Route Savvy
Stick to a fairly short, well-lit loop. "Winter brings slick and icy conditions plus less light, which can hamper your ability to see and be seen," says Jason Glowney, M.D., an internist with the Boulder Center for Sports Medicine in Colorado. At night, wear plenty of reflective gear and always run against traffic. If possible, run into the wind on your way out and with the wind on the way home. Running into the wind when you're sweaty will subject you to much greater stress and cold exposure, warns Glowney.
Do a Good Warm-Up
Take a few extra minutes to get your joints and body loose. Do your warm-up indoors, if possible, and focus on dynamic stretches like leg swings and walking toe touches, which warm muscles quickly.
Think of Your Lungs
"Cold, dry conditions make the respiratory system work harder since it has to warm the air you're breathing," says Glowney, who is also the team physician for the Garmin-Transitions U23 cycling team. To protect yourself, cover your mouth with a balaclava or ski mask to hold in your body's existing warmth and humidity.
"Winter months tend to be drier, and athletes may be less aware of the amount of sweating that's actually occurring," says Glowney. The cold makes you feel less thirsty, but your body is still sweating so you need to diligently replace fluids, just as you would in the heat.
Have a Goal
Pick an early-spring 5K or 10K and use it as motivation for when the cold months make outdoor running seem unbearable. If you're looking for a race or running club near you, Road Runners Club of America ( rrca.org) is a great resource.