As already said, driver ability, or at least experience driving on snow is key.
The obvious one is to slow down and do everything as smoothly as you possible can. Traction is key. If your wheels start to slip through acceleration, cornering, or braking then back-off, regain traction and try again more gently. You should expect to have to correct things frequently like this, so anticipate it and allow plenty of additional space and time.
Winter tyres and/or 4WD most certainly help, but they are not a panacea. That is especially true when it comes to braking. All cars have 4 wheel braking so you are no better off in a 4WD, slow down and brake early and gently. Engine braking is essential, particularly if you are going downhill, don't forget that engine braking can still cause the car to slide, particularly if it's a sudden shift. If you drive an automatic make sure you know how to change gears manually, it really is an essential skill on snow.
If your wheels start to slip when accelerating, do not step on the gas harder and try to power your way out of it, you'll just end up sliding into the gutter (or if unlucky an oncoming car). Lift off, and try again more gently, perhaps try a higher gear, don't worry about speed, focus on keeping your drive wheels turning without spinning. Be aware of whether you are driving a FWD, RWD, or 4WD car, they all react differently when you lose traction and it helps knowing what to expect.
The bottom line though, no matter how capable you are, or your car is, if the road is blocked by other cars you are going nowhere.