Winter tires are the single biggest improvement you can make. Their compound stays soft in the cold and their sipes grip snow in a way an all-season pattern cannot match.
Whatever you are on, do everything gently. Accelerate softly to avoid spinning the wheels, brake early and progressively, and steer smoothly - abrupt inputs are what break traction.
Leave far more space than usual. Stopping distances on packed snow can be several times longer than on dry tarmac, and ice can be longer still.
Watch for black ice on bridges, in shaded corners and in the early morning. If the car does start to slide, ease off the accelerator and look where you want to go rather than at the hazard.
Check pressures more often in winter, because cold air contracts and pressures fall.