For driving: If there's snow on the ground and you're in a safe place to do this, get up to 5 mph or so and slam on the brakes. That'll give you a good feel for your much traction you have. Of course, conditions vary, so don't sue me if you had grip on your home street but not the freeway. Other than that, keep acceleration to a minimum, and I mean that in any direction. Ease on the gas, ease on the brake, slow down BEFORE you need to turn, and turn easy. Be calm, a panicked reaction to a slide can make it worse. Abs and traction control can save your ass, but they're emergency systems. If they are activating frequently, SLOW THE FUCK DOWN.

Driving aside, nice winter clothes are great, but how you wear them is much more important in my experience. Keep body heat in and cold wind out. Assuming that your clothes actually fit, the best, free way to do this is to simply tuck your shirt into your pants, and if you have them, coat sleeves over your gloves and neck gaiter into your coat. You lose so much heat in those areas, by addressing them you can be out many degrees colder before you need another layer. However, if you're physically exerting yourself in the cold, don't let yourself sweat, because as soon as you stop that shit will freeze. Be mindful of when you start getting warm and be prepared to untuck clothes, open vents, or remove layers.

Finally, and you should be doing this anyway but people forget in winter, drink plenty of water.