Four Wheel Drive Concepts
Offroad Driving Techniques
   Basic driving skills
   Climbing steep slopes
   Descending steep slopes
   Traversing steep slopes
   Driving in mud
   Driving in sand
   Driving in snow
   Wading through water
Vehicle Recovery Techniques
Off-Road Driving Techniques
Snow Driving
The first key to effective snow driving is a light throttle and choosing the correct tyre. Driving in snow requires a tall tyre with a narrow section-width. This allows the tyre to cut through the crust and obtain traction on the hard surface beneath the snow (the opposite of sand tyres).
Snow driving   Traction can be enhanced by siping the tyres. Sipes are little razor cuts across the tread blocks which increase the number of biting edges on the tyre. Studded tyres are another effective solution. For deep snow, use snow chains or cables. If you only have one set, always put them onto the rear wheels (note that on a front-wheel drive 2x4 you'd put them on the wheels under power, i.e. the front wheels).
You could try throw some bags of coarse-grain sand into the back as ballast weight, which you can also use to help you get unstuck later. A shovel is another handy addition.
If you're driving a permanent 4x4, keep the center differential open. The last thing you want is four powered wheels all at the same speed intent on going in different directions. So, do not lock the center differential, as then only the misbehaving wheel is pulling towards the ditch, instead of all four. However, as many modern SUV's have part time four wheel drive (4x4 locked or 2-wheel drive), you make do with subtle and ginger throttle and steering inputs while in four wheel drive.
Lastly, avoid revving the engine, go into low range in deep snow, and, as mentioned above, use a very light throttle. This will encourage the tyres to bite and grip rather than spin without grip.
Snow Tyres
A good snow tyre is not an open-lugged design like a mud tyre. It is moderately open for self-cleaning, but close enough to compress the snow inside the tread and use it's cohesion to supply traction.
Snow Terrain Tread Pattern
Snow tyres also use sipes and kerfs. A sub-class are tyres that are rated M&S (Mud and Snow), which have some potential as a pseudo AT, but dedicated ST's wear quickly on dry roads.
Tyre Pressure
Maintain on-road pressures. However, in severe off-road snow conditions a reduction to 60% of standard on-road pressure may prove beneficial.