One trait of a "master coach" is the ability of decomposing the sport down to a set of basic elements (skills or movements), then naming these to ease communication (preferably Using Vivid Images. The sport should be then explained in these terms; the basic elements practiced to perfection and then composed back into the larger elements of the sport.
While great skiing can be simply described as "tip your skis on edge and balance on the outside ski", I feel a few more basic components are required to successfully communicate: teach, feedback and discuss.
The following is inspired from several systems, including PMTS, CSCF and the USSA. The possible values for each dimension are given as well. These organizations are oriented towards performance skiing and more or less talk about the same concepts (there are only so many ways to ski well, right?).
|S - Stance||('-' too narrow, '+' too much)|
|M - Movement||('-' too little, '+' too much)|
|T - Tipping or edging||('-' too little)||('e' early, 'a' late)|
|F - Flexing||('-' too little)||('e' early, 'a' late)|
|CB - Counter balancing (hip angulation)||('-' too little, '+' too much)||('e' early, 'a' late)|
|CA - Counteracting (separation)||('-' too little, '+' too much)||('e' early, 'a' late)|
|FA - Fore/aft||('-' too back, '+' too forward)||('e' early, 'a' late)|
|I - Inside ski||('-' too little, '+' too much, 's' shuffled)|
|P - Pole plant||('-' too little, '+' too much)||('e' early, 'a' late)|
A stance that is too narrow ('-') causes the legs to get in the way of each-other, while a stance that is too wide ('+') causes all kinds of bad effects, like too much weight on the inside ski, slow transitions etc.
Read more in Skiing - the wide stance debugged and these sessions:
Stability with mobility is the mantra - we need to continuously move on skis: the more powerful and faster we go, the more we need to move. This is not a skill in itself, it is more a summary of how active one is on skis and it is reflected throughout the other elements.
Some are too static ('-') and are bounced around and cannot be in balance, while some have too many useless movements ('+'). So, a feedback of "you are too static" can easily be addressed by moving more... I may get some flak for this, but I think any kind of movement is good to get someone exploring the ranges of motion and become more confident on skis, even if the movement is technically "wrong" in the beginning, like moving up and down.
You can move up and down, by extending or flexing… or moving sideways by angulating at the hip or rotate the upper body from the hips, or even incline the entire body.
Every good turn starts with tipping and ends with tipping: we end the turn tipping the other way or un-tipping if you want. I prefer this PMTS term to edging as it is more explicit on how we get there: by tipping the skis on edge starting from the ankles. Tipping happens in time, so it can be too early ('e') - i.e. untipping too early, when the turn is not completed or ended too early; or too late ('a') - where tipping occurs too late in relation to the fall line.
Insufficient tipping results in small angles and large turns for the speed ('-') requiring skidding or steering to get the desired turn shape, perhaps a result of not flexing enough (F-): if the legs are long, you can't really tip the skis without dropping the hips into the turn, which takes time and most likely results in inclination or hip dumping.
Too much tipping ('+') results in a loss of balance and... wipeouts?
We flex to release the skis and transition. Extending ('-') in transition results in losing control over the movement (gravity takes its own good time to bring us down); loosing contact with the snow and thus a loss of control; impossibility of tipping early enough and other side effects.
Too much flexing ('+') basically results in dropping the hips (inside the turn?) or unsafely below the knees, being stuck in the back seat etc.
As we tip the skis on edge, we counterbalance to maintain balance, given the speed. Counterbalance happens in time and is metered, corresponding to the tipping of the skis on edge.
We counteract the turning of the skis by twisting the upper body the opposite way, from the hips. The result is "separation" or "quiet upper body" - as the upper body appears to be still while the skis are turning.
Since we just counteract what the skis are doing, when the skis turn or glide sideways during the transition, the upper body simply looks "stable".
Too much and too early counteraction is a classic cause of hip dumping.
The Fore-aft refers to good fore/aft balance, being forward. The most important time to be forward is at the top of the turn, when we're trying to engage the edges and bend the skis. Also, throughout the turn, you have to be forward as much as you want the skis to turn - as soon as you fall back, the turning radius will be reduced.
We recenter in transition, and use ankle flexion together with pulling back the inside ski during the turn to manage fore/aft.
Not forward enough ('-') and too far forward are the two obvious possibilities here. Too far forward cause the tails to wash out while not forward enough will not engage the tips of the skis sufficiently and we'll understeer.
There are cases when being forward at the end of the turn causes the tails to washout - that would mean "a" - too late.
We pressure the outside ski much more than the inside ski - where this is lacking ('-'), trouble ensues. By contrast, the inside ski should be light and away from under the body, to the side.
There are cases where too much weight on the outside ski ('+') is troublesome, for instance when skiing powder.
The inside ski should not shuffle ahead of the outside ski too soon into the turn ('s'), but only when the turn and slope warrant it.
Read these articles for more details:
The pole plant can be either missing or inconsistent ('-') or involving too much body movement and possibly rotation ('+'). A late or early plant is also an issue that can be quantified.