what do you mean up a "ski hill"? what actually goes wrong...   is it when you get started or are you going ok and then get to a point where its too steep and it starts slipping?
you want to keep the and avoid wheelspin, so if its a manual and you can't get going try starting in second or even third and shift way early.   if the road is just too steep and a good set of snow tires doesn't do it, you'll need chains... they will get you up anything.