Here's a really cool advanced drill, that I think is called "the Penguin":
Leave the poles and let your arms by our sides, with the wrists touching the hips. While keeping the arms in place and the wrists touching the hips, get big angles and try to touch the snow with the fingertips.
As a progression to it, if the failure rate is too high (probably it would be) you can use "fun carving" where you touch the snow without locking the hands in place. Also, another progression is to ski and try to get big angles with the hands locked behind your back.
The trouble with the "fun carving" is that it leads to a certain amount of inclination, in the drive to touch the snow, which is not very good, so use this drill sparingly. The penguin instead shifts the focus to driving the hips down.
It's essentially a range of movement drill. Use it to show the range of movement needed, to someone lacking it.
But, you have to have a lot of advanced technique and time it properly, for this drill to work, so it can be used as a guided discovery tool for other skills: try the penguin and have a big failure rate. Then talk about say counterbalancing and spend some time drilling it and then try the penguin again, while asking the racers how can they get bigger angles.
It's instant feedback: you play with a movement, fail and have an instant feedback and try again in the next turn. If the failure rate is still high, pick up another skill and introduce it / drill it and then go back.
The external cue of touching the snow with the fingers provides a clear measure of success as well as an external focus, which allows to improve other skills while doing this drill.
There are many uses for this drill.
Also, do not abuse this drill by attempting it too often - it does have quite a few drawbacks of its own, like putting them more aft and messing with the turn sequence by focusing everything on deep angles too early.
Read more drill ideas.