There are lots and lots of instructional videos, and I watch them. However, this is the video I go back to all the time, one of Mikaela Shiffrin training.
I watch the quietness of the upper body, the extensions, the angulation, the agility and quickness, the earliness of the turn, where the belly of the turn is by where snow is kicked up, the transition. I watch it over and over and over and over, visualizing myself doing it, to the point where I experience my muscles micro-contracting while I watch. Everything I see in this video, I use, in powder & crud, on ice, in steeps, bumps, and trees.
And, here's another video,
I've studied it over and over too. When you look long enough and compare the two in the minutest detail, you see the differences and have ah-ha moments.
Yes, it's helpful to watch an instructional video explain how to do something. But, short of actually skiing, I think self-visualizing while watching high quality skiing is the closest thing to practicing.