I grew up in the south where cold is "put a sweatshirt on until noon" and then it will have heated up enough to not be an issue.
Having been in DC long enough, I should know better and winterize properly, but I almost never do.
Think about winterizing your car. Also, something I never do but always need to. You change the oil to a lower temperature oil, you either put air in your tires or vice versa (never remember), and you keep that handy dandy heated ice scraper in your glove compartment (check!). You do these things because the cold is a little harder on your car than the summer.
Well, the same is pretty true with winter and your body. It might not seem like it. You always here about people worrying about working out in the summer (or maybe that's just the south.) You have heat stroke, heat exhaustion, dehydration, etc.
But in my experience, no one really talks about winterizing.
When it's cold outside, remember the following tips:
1) Warm up and cool down longer than normal. Your muscles will take longer to warm up and shorter to cool down. Both can cause injuries. Two examples: stretching a rubber band that's been in the freezer doesn't work very well. Likewise, if you put a hot plate into a cold freezer, you run the risk of a crack forming in that plate. A wise decision is at least 7 minutes on both ends.
2) Stay hydrated. It's hard to remember this one because your body doesn't give you the same cues it does in summer. When it's cold outside, we give off a lot of moisture. It's why your skin gets so dry in the winter. Keep a bottle of water around and try for at least 3 of them a day. 4 is your best bet. See what happens to your winter skin!
3) Related to (1), make sure you have warm gear on before and after you go out to go to the gym. Between home/car and the gym, keep sweats, jackets, hats, gloves, etc. at the ready, especially when leaving. You may have cooled down enough, but keep the benefit of the stretch that you got by keeping your muscles warm! If you're working out outside, don't just run out with shorts and a long sleeve shirt. Even if you're the type of person who gets to that point where it's too hot, please consider long running tights or a jacket you can take off and tie around your waist. Major injury prevention here!
4) Wear sunscreen. Just becasue it's cold doesn't mean there aren't UV rays out there. Protect your skin and get the added benefit of moisturizing dry winter skin. Find a good basic body lotion with an SPF of at least 15 for winter days. ESPECIALLY your face.
Finally, this isn't a winterizing tip per say, but it's important in the winter---
Don't let the cold weather and holiday season keep you way from staying active. Trust me when I tell you, you don't want to be huffing away on the treadmill Jan. 2. You'd rather be one step ahead of everyone who enjoyed the pie but didn't work it off.