With in 8 or more inches of snow headed out way with Nemo and us not having much snow for a few winters, lets go through some tips. First no matter what you drive, drive slow and easy. 4 wheel drive doesn't help you stop,...leave more distance and slow down. I see more SUV's off the road than cars. Once a car is moving it typically handles better than a top heavy SUV. Once an SUV gets moving on the snow, its still big and heavy.
Dress for the weather. If you get stuck you don't want to be in a short sleeve shirt and sandals. If you get stuck, build up a rocking motion, back and forth. Don't spin the wheels very much - you will burn out your transmission and dig yourself in deeper. Forward, reverse, forward easily until you build up enough momentum to keep going. In a 4wd - learn how to go into 4wheel lock and low range if you have it (many trucks may require you to be not moving and/or in neutral - check the manual BEFORE you need it). My best piece of advice, no matter what you drive, is throw a shovel and towels in the car - shovel any high spots under the car, snow under the car holding the car up off the wheels is the biggest reason for getting stuck). Shovel the snow around the wheels -- make enough room to let you build up a forward and back rocking motion (the towels? mostly for you being wet and sweaty by this point and needing someplace to throw a wet dirty shovel).
Its always a good idea to keep moving. Getting a car moving from a stop is the single hardest thing to do in the snow. If you can let the car creep along at 2 MPH, its much easier than starting from a stop. Try to stop facing flat or downhill, not facing uphill. Of course while going uphill getting started is your problem, going downhill, stopping can be like ice skating.
Plan your stop early around cars and especially when coming up to stoplights - you dont want to slide into an intersection and oncoming cars. In fact, when your light turns green, make sure you look both ways - just because the light is Red for oncoming cars, doesn't mean they all can stop in the snow.
Make sure you have at least 3/4 to a full tank of gas, decent tires (I guess its too late now if you don't, right?), that the air pressure is normal (or a little low) NOT HIGH (low pressure helps build traction - high pressure makes the tires harder). BTW, the gas in your tank helps in two ways - most cars have more weight over the front tires than the rear - at 7lbs a gallon the 150lbs in the rear helps the rear tires do more work. Throwing a couple of 50lb sandbags in your hatch or trunk doesn't hurt either, but don't overdue it as some point you'll just make the car/truck lower and increase the chance of getting caught up in high snow.
If you get on ice - try to get off the brakes, move 6 inches or a foot and a half to your left or right, and try the brakes again - the surface could be rougher or have more snow on it. If that doesn't work - try it again, even moving back where you were it could be different as you move on. Typically, the best place in near the shoulder - while people may have turned the center into ice, the sides could have more snow which is easier to stop in than snow.
With 8-12 inches or more, I wouldn't even consider going out in a RWD (Rear Wheel Drive) car - yes I know your BMW may have traction this and that. That helps to keep the tires from spinning - but it doesnt change the laws of physics. No matter how many electric nannies you have, in most cars roughly 55% of the weight is on the front wheels, 45% on the rear. With RWD and snow, it is very difficult to push 100% of car with 45% of the weight on the two wheels doing the pushing on slippery surfaces.
Just to show that my methods work, two or three years years ago when we got pounded, I threw a shovel in my fwd car and went out to get my exs friend in a 4wd Toyota Sequoia. I was able to get her out of 20+ inches of snow by shoveling out around the wheels and instead of her drivng and just spinning the wheels, rocking the truck to get enough movement to get the truck moving and keeping it moving out of the big snow it was stuck in.