More experienced skiers than I am have said that they never stop learning new things, noticing new details about their sport. So I feel safe in saying that I constantly notice things about technique as I slide along.
Maybe I knew them once, forgot and rediscovered them. No matter. It still feels fresh and fun.
Since I really developed any refinement as a classical skier only in the last eight of my 24 years skiing I'm constantly looking at different ways to slice and dice the movements.
In classic much more than in skate, things have to happen in opposite and simultaneous rhythms of balanced movement. A skier this week said that his experience as a swimmer helped because his brain was already accustomed to coordinating bilateral movements of this sort.
One difficulty in conveying technique to a beginner is that you have to tell them where to start when it all really starts at once. Even the tried and true method of skiing first without poles demands balance and an element of timing. it also requires that the skis be fitted well enough to allow grip.
Next a skier will be taught about the kicking leg and the gliding leg. That's where the description becomes inaccurate for the sake of clarity. The kicking leg is generally initially described as the one stomping down into the snow as the weight shifts to the other ski on the "gliding" foot. But the key to smooth, strong classical skiing, even up hills, is to kick the gliding foot forward as the stomping foot kicks down. So there are two kicks that have to happen simultaneously.
Kick the gliding foot forward before you shift weight, but only a moment before. It works best when you feel like you are slightly behind your gliding foot and shift forward onto it from the ground up. At the same time your opposite hand is shooting forward as if it pulled the foot. As this happens, your weight rolls forward to the ball of your stomping foot as your heel comes up because you have shifted your weight to the now-gliding ski. The pole on the stomping side has swung back as your hand swings back and reaches the end of its arc as your weight is fully committed to the gliding ski.
Once you master the basic shuffle, an instructor will give you various tips to help you remember how each portion of the motion should feel. "Pretend to kick a ball down the track." "Pretend you're sliding on a hardwood floor in our socks."
In poling, the teacher might say you should swing your hand forward as if you were tossing a horseshoe, in an underhand motion that ends with your hand fairly low compared to where you might think it should be. One also suggests bringing the hand forward as if gently tugging a recalcitrant puppy on a leash to get people to think more of bringing the hand smoothly forward than of jamming the pole tip in the snow and shoving themselves along.
The key to kick is proper weight shift. That's why so many instructional exercises force the skier toward full commitment to the forward swing of the appropriate appendage. If your weight is in the right place, you will have positive kick and can therefore throw yourself forward again with a strong glide.