I think everything has pretty much been said, so I'll basically just second (or third/fourth/etc) everything.
SLOW DOWN. This cannot be overstated.
Get proper snow tires. AWD = go, snow tires = turn/stop. I felt safer in my Civic with Blizzaks than my Outback with all-seasons. My stopping distance was 2-3 times longer in the OB with AS vs the Civic with Blizzaks. Nowadays, I've turned through icy intersections where other people slide, and due to snow tires, AWD, and DRIVING SLOWLY, I didn't slip at all.
PRACTICE. Whip the car around in an EMPTY parking lot to see how your car handles in the snow. Break it loose, regain traction. Learn how YOUR car with YOUR tires handles. To get the general idea of what you're supposed to do, go play a racing video game where you have to drift and then straighten out (Forza, Gran Turismo, etc). It's the same principle, just on a surface with less friction, less speed, and less supercars :-(
Assume everyone else is speeding in a RWD muscle car with summer tires. Somehow, even in New Hampshire, people forget how to drive in the snow. Case in point:
How In Snowhell Could You Crash a Car Like This? (Updated) By assuming everyone else sucks (or is using the worst snow equipment possible), it keeps you more alert and aware of your surroundings. When someone else loses traction and is going to hit you, there's (usually) nothing they can do about it, which means you need to be ready.
After the light turns green, wait an extra second before entering the intersection. Seriously. Sometimes, the light changes, and normally you'd have to hit the brakes hard to stop in time. Sadly, on the snow, that doesn't work as well, and IF you were able to stop, you'd be in the middle of the intersection. When you hit the brakes and nothing happens, you just have to keep going. At that point, it's about going on the correct path and not hitting anything, and less about the red light.