Be Prepared
Check your washer fluid and replace it with the anti-freeze stuff. You can find this all over the place in colder climates starting in about October. Start putting it in then so that by the time winter gets started in earnest, you've got a good concentration of it in the tank.
Make sure your wipers are good. Nothing shows imperfections in wipers like snow. Watch them carefully in the rain and, if you see streaking, replace them.
Get a kit together. Actually two kits. The first for everyday and the second for any trips you have to make in the winter. The first kit can be simple: ice scraper/snow brush combo, cell phone and charger, non-clumping kitty litter. The second kit is the first kit plus some blankets, a few non-perishable food items, a deck of cards and some sort of shovel. If you're traveling in a well developed area on major roads there's not much need for an emergency survival kit since you're probably one phone call from rescue and, if you get really stuck, you're going to be towed out. But if you're off in the middle of nowhere you could do worse than to have those handy.
Know your limits.
Get to know your car and how it handles (or doesn't) in the snow. Church parking lots can be great for this (ask first). Just go out, do some doughnuts, put it into a skid and get out of it, break way too hard for the conditions, and overall just have fun (it also helps to offer to clean up afterwards, if you can. The intern/youth pastor/facilities guy would love to have someone help them spread salt in the cold).
Consider why you're going out and, if possible, don't. There are very few reasons to go out in a class 3 snow emergency and most of them would be better served by calling 911 and letting them come to you or by walking next door and bumming some grub or TP if you were caught totally off guard. As the conditions improve, the reasons need to be less and less, but at least give it a good thought.
4 wheel drive is a blessing and a curse. At low speeds it distributes torque to 4 tires instead of 2 so you have a better chance of getting grip and getting out. However, once you're up past first gear, it's actually taking the torque you need and distributing over 4 wheels what would really be handy to have focused on 2 (especially the front ones). So the faster you go, the worse 4WD is for you. Also, even if 4WD did offer you better steering and better acceleration at high speed in the snow (which, in super optimal conditions, it may), you still don't have the power to stop and faster than anyone else. And everyone else isn't going slow because they can't go faster, it's because they know how hard it will be to stop if they do.
Be aware.
When driving you should know what cars are around you, have an idea what's coming up and be forming plans on what to do if things go wrong. And things will go wrong eventually. Knowing there's an empty spot in the lane to your left just behind the black SUV might save your bumper if the car in front of you has to stop suddenly. Knowing there's a snow bank to the right and oncoming traffic to the left gives you a good idea where to try and steer if you can't stop (hint: go for the drift).
Traffic reports are handy, but turn off the radio otherwise. Listening to the engine and road noise can often give you a split second of advanced notice that things are going wrong. If your engine starts to rev, you probably need to back off. If you start hearing slush hitting the bottom of your car in a different way, it's safe to say conditions have changed and you may need to adjust accordingly. Passengers screaming from the back seat could indicate that you're about to be hit by a speeding snow plow. That, or you you need better friends.
And, yes, texting and talking on the phone while driving is pretty much a bad idea anyways, but it should go without saying that in adverse conditions it's even worse. Unless someone was calling you to tell you about something that could prove to be immediately fatal (like a ninja assassin in your back seat, for instance), your driving takes precedent. Put it on silent and check for messages when you arrive.
Consider the other guy.
Most accidents in bad weather are caused by the other guy. Don't be that guy.
Drive with traffic, at the same speed as that traffic. If you're not comfortable with the speed of the highway, get off and take a back road. If you're going way faster than everyone else, slow down. Even if you can handle it, making everyone adjust to your speed can cause more problems. Also, if someone pulls out in front of you going much slower you're going to hit them and then nobody wins. If you do decide to pass be careful and refer to the next paragraph...
Stay in your lane. Changing back and forth between lanes is annoying in normal traffic, but in bad weather it's just one more thing that every other driver must now adjust to, so don't do it. If you must, signal way in advance, let them make you a hole (they should in this weather) and then merge over slowly and deliberately, preferably on a straight section of the road.
Clean your car. You're surely not dumb enough to be the guy that only clears a small portion of the windshield so you can see out. But besides the windows and windshield, take time to do the hood, the roof and the trunk lid. You'll appreciate not blowing the snow on the hood into the windshield and the folks behind you will appreciate not being behind a rolling whiteout on the onramp. This goes double for vans and trucks who can lose huge chunks of roof snow all at once. One of those hitting the road in front of a skittish driver might be all it takes to send them out of control. Also, take the 1.4 seconds and wipe off your headlights. Everyone else will thank you.
Now that they're clean, turn on your head lights. Look at the cars ahead of you. Notice how the cars without lights kind of fade away after about 100 feet? Don't be those guys. Also, while we're here, use your turn signals.
Leave good following distance. Remember the two second rule? Make it three or, better yet, 4. If possible, stagger with the lane beside you so that the car over there and slightly in front of you can jump over if he needs to. And when someone does get between you and the car you were following at a healthy but not do distant pace let off the gas, let the space between you increase and then resume following.
And as a corollary, if someone is following too close to you...let them pass. Yes, you're in the right, but that's small consolation when you're picking pieces of SUV grill out of your hair.
That's about all I have, really. I'm sure there's more, but seriously, be careful out there and try not to do anything stupid.
