A few years ago, I wrote a post about winter running, especially in New England. Quite a few people seemed to appreciate it, and I've recently started talking to other runners more, so I figured I'd try to fill in some of the gaps that I forgot to address then. Warning: a lot of this is "works for me" personal opinion. I'm sure there are other runners who would disagree on many points. Apply grains of salt accordingly.

Gait
Yes, you should get used to the idea of running a bit differently than you do in summer. The first part should come pretty naturally: shorter steps. A lot of this has to do with keeping your center of gravity over your feet. The slipperier it gets, the less you want that center of gravity to be out past your feet. This means you will also want to pay close attention to body angle. Another natural inclination on a slippery surface is to keep your feet low, which often leads to a hunched posture, but I find it's actually better to keep the body very upright. The difference becomes particularly noticeable when running up or down hills - not that you want to be doing too much of that anyway, but a bit is unavoidable. If you lean too far forward going uphill, one slip could land you on your knees or hands or face. If you lean too far backward going downhill, you're even more likely to end up on your ass. Your foot will slip occasionally, it's just a fact, so your goal should be to ensure that your momentum carries your center of gravity smoothly through to the next step.

Speaking of slips, more aggressive runners might also want to avoid a strong toe-off and long stride on anything but obviously clear surfaces. I know, you've probably invested significant effort into learning to run that way, but if you're pushing too hard and there's not enough traction your foot will kick up pretty strongly and that can throw you off balance. Remember, if you get injured your pace will be zero for a while and still slower thereafter. Save the speed heroics for better conditions.

Choosing a Path
Road or sidewalk? That is the question. The answer really depends a lot on specific circumstances. Sidewalks are preferable when they're clear, but that's too rarely the case and even more rarely possible to determine when you're on the move. If it snowed recently and someone cut a path with a snow-blower that's great, but how long will it last before you hit the property line and the next homeowner didn't do the same? Or until you get to the next intersection to find that the plow left a huge pile blocking the sidewalk entry/exit? To know that you have to be able to look a decent distance ahead with good light, and that's just not always possible. If you can tell, go for it. Otherwise, I'd really rather run in the road which tends to be more thoroughly cleared and salted. There might even be the remnant of a bike lane so the cars aren't getting too close. Nowadays social distancing is also a concern. Where there are a lot of walkers, running in the road while they stay on the sidewalk helps keep everyone further apart. It's not like you'll be contending with many cyclists. Of course, you have to follow all the usual rules for running in the road - be on the side with visibility, know where your nearest bail-out (usually a driveway) is, etc.

Another thing you might be tempted to do is cut through a parking lot. For example, there's one spot on some of my routes (near Neillio's and Busa for my Lexington friends) where the parking lot is often clear but the sidewalk is not. Cutting through is a fine idea, but run in the center to minimize the risk of a car pulling out into you. Drivers often don't even look for walkers entering their path as they're backing up, let alone runners. It's tempting to stay near the edge as you would (mostly) do on the road, but in a parking lot that would be a mistake.

OK, next question: if there's a strip of dark pavement on an otherwise snow-covered path (Lexington friends: especially common on the bike path), which do you go for? As with sidewalks, if you can clearly see that the dark patch is completely dry, go for it. Otherwise, that dark patch could be hiding black ice and you'd be better off on the hard-packed snow. You'd be surprised how well black ice can hide itself. The one time I've fallen while running in winter, including some 5km runs that have been icy from end to end, was on pavement that looked merely damp, not wet. Didn't even realize I was at risk until my butt hit the ground. Fortunately it was a side street with no traffic. As you run you'll develop a pretty keen eye for the ground ahead, and also a memory for where the trouble spots are, but still better to err on the side of caution. Even if you do slip on snow, it probably won't be as sudden (or as hard) as ice falls can be.

Shoes
Shoes do matter. A lot of people think it's because you need to keep your feet warm, but at least for me that's certainly not it. The only reason I wear thicker socks in winter is to keep my ankles warm. The part of my foot inside the shoe has never gotten cold, except for the few times I've gone out when it's 10°F or less - and that's awful for other reasons. The reasons I think winter shoes matter are:

• Traction. There's really a big difference here. I had one pair of winter shoes, unfortunately no longer made, that I called my "gecko shoes" because they'd grip the floor in my mud room so tightly. That's a good thing when you're on wet (but not frozen) pavement, or you've just run on snow or slush so your soles are wet even though the current pavement is dry. As with tires, a good winter rubber/synthetic outsole will still grip pretty well. A lot of summer outsoles just won't.
• Water/slush resistance. Pretty self explanatory. You will get water or slush splashed onto your uppers, and even your lower legs. (Random note: this is why I wear socks outside of tights instead of the other way around, because I never re-use socks anyway.) Wet feet suck.
• Cushioning. Nobody ever seems to think of this, but I can attest that it's real. Every midsole compound will lose elasticity when it's colder. That's just physics. A compound designed for the perfect amount of "give" at warmer temperatures will be too stiff when it's cold. The compounds in winter shoes are designed to hit that optimum when it's cold, which is better for both comfort and injury prevention.

For all of these reasons, I think a separate pair of winter shoes is worth the investment. Besides, as long as you're wearing them you're not wearing your summer shoes, so you'll get more wear out of them later. It all evens out. FWIW, I'm usually an Asics or Brooks fan but I'm currently wearing Saucony "Peregrine 8 ICE+" shoes. Early days, but they're off to a very good start. The selection of winter shoes tends to be pretty thin and models never seem to last long, so you'll probably find yourself brand-hopping more than for your three-season shoes.

Lastly, what about micro-spikes? I have 'em. I hate 'em. If you're running entirely on snowy trails with dirt underneath then maybe they're the right thing, but if you ever have to traverse dry pavement - i.e. every run, for most of us - they'll chew everything up. That's already bad, but they'll also feel lousy and wear out doing it. Because they chew everything up, they're also a pain to put on and take off because you'll want to be doing that outside. I just find that I never use them, even on the snowiest days.