Some excellent advice above, especially Martin Vikings post.
Couple of points to add though.
Whilst diff lock is a very useful thing, sometimes it can be counter productive, when in use obviously both drive wheels will spin together, this can induce the drive axle to swing out of line especially if the road is cambered, in some circs allowing one wheel to spin (invariably the spinning wheel will find grip and its opposite number will then spin up) and cut through the muck whilst the non spinner keeps the lorry straight is better…its all a learning curve and there’s no hard and fast rules here.
Diff lock shouldn’t be engaged when the wheels are spinning, ideally when stationary but can be engaged when moving so long as the drive wheels are turning at the same rate.
Get used to driving your vehicle in manual mode regularly, too late to learn the gears and the gearbox idiocyncrasies when the snow’s down.
If you have a lift axle dump the air and hopefully lift it entirely to get as much weight onto the drive axle as possible when the speeds are low and spinning up is likely, similarly if you are approaching an iced hill, be prepared to dump the mid lift air as soon as the speed drops low enough to allow it…experiment with the device so you know exactly what speed is involved, it might make the difference between ascending a hill or not.
If you have a lifting front axle on a trailer, make sure the device is switched on (usually a air button or switch) so the axle raises when the load is light enough, bit more weight on the drive axle.
Check how your trailer lift axle works, on some of ours even without switchable lifters if you drop the trailer suspension fully down the lifter will raise even if the trailer is loaded (try yours now so you know if its an option or not when stuck)…you shouldn’t drive anywhere like this obviously but it might prove useful to transfer some more weight onto the drive axle to get you up an iced slope in a yard, or a steep hill on the road if you stop immediately after and re-inflate…don’t tell 'em Pike.
Most important this…Traction Control/ASR…this is the thing most likely to stop you getting up a slippery slope, soon as the system senses a drive wheel spin it will cut the power, which might well trigger a gearchange if in auto, which will then immediately spin again in the power gear again triggering a power cut, result stuck.
Turn off TC/ASR, experiment turning off before you need to do this in desperation, typically as you approach a steep slippery hill, so you know what effect it has…not suggesting you drive down a twisty slippery road without ASR/TC necessarily but turned off at the appropriate moment can keep you going.
Learning your lorry as much as possible is always a good thing.
Whenever possible make sure your load is weighted towards the drive axle being up to max weight, TBH this is good practice on most vehicles especially artics at most times, lessens chances of the tail wagging the dog.
Gentle inputs on all controls, the most important thing is to keep moving if at all possible, keep a good distance from the vehicle in front, just because some hero in a lorry goes past everyone in the third lane of a three lane motorway doesn’t mean you can, this is a favourite practice of some foreigners but they well have a full set of winter tyres fitted and be able to do this quite safely even if its wrong.
Most importantly, keep your lights windows and mirrors spotlessly clean inside and out, chances are you’ll be doing some ducking and diving in poor visibility, the more you can see the better your chances of pulling through.