"Over coaching,"

You can "over-coach" an athlete.  Athletes don't need constant feedback from a coach unless they "true" beginners in the sport.  Skiing is a feeling, and being good at ski racing takes experience.  Many times, just setting up gates and allowing your athletes to just run the course, will provide them with enough feedback if they have racing experience.  Be conscious of providing too much feedback.  One unsolicited technical pointer a training session should be enough.  Get used to asking questions such as "what are you working on this run?" or "how did that run go?"  "what did that run feel like?"  "did you do anything differently than last time?"  It is important to remember that from the athlete's perspective, skiing is a feeling.  An experienced athlete can feel where they lose speed and where they gain speed.  They also can feel how the force of gravity interacts with the body, and how their body reacts to the forces as they descend down the hill.  They may need a little more direction when it comes to line choices, however when it comes to technical aspects of an athlete's skiing, it is difficult to make adjustments without knowing exactly how it feels for that skier to ski through a course.  Here is an example of what I mean, observe the following video:

If you watch closely you can see that Grandi switches edges so quickly that he doesn't find the platform before he moves from turn to turn.  It is easiest to see when his skiis are slightly airborne.  The problem with not finding the platform first is that it is difficult to transfer all the energy from one turn to the next.  Now the truth is that in SL, you really don't need to do this because of the rapid turning nature of SL courses.  There is a lot of steering used in SL and it is very easy to get a lot of impulse from the skis.  The impulse will help transfer the energy from turn to turn so you don't necessarily have to transfer all the energy in order to make a fast and efficient turn.  As Grandi's coach, you could tell him to be more patient and find the platform first before he switches edges, but is it all that necessary?   From Grandi's perspective, how does it feel to ski in an SL course?  Does he need the extra energy created from finding a platform first?  He might find that gets enough energy transferred from turn to turn already.  If the coach emphasizes this unnecessarily, it would be "over-coaching."  Another example can be observed in the photo below:

From the observer's perspective the skier in the photo above appears to be skiing in the "backseat."  As their coach you might be tempted to try to get that skier to move a little farther forward so they feel more pressure on the front of the skis.  This photo was actually a screen shot taken from world cup SL footage.  I don't know who the athlete is, but if they are in the backseat, it works well for them.  If you saw the rest of the footage, you probably would agree that this skier doesn't have issues with their stance.  It would be like trying to correct Bode Miller's interesting approach to stance.  It may not be all that necessary and could be "over-coaching."

How do you know when you are over-coaching your athletes?  First thing I would consider is not giving unsolicited feedback, especially to experienced athletes.  Get used to asking them how it went from their perspective.  For example if you have an athlete who flies down an SL course in the backseat, but still makes all the gates.  Ask them how it felt.  They might say:  "great!" and in that case you might have the next Bode Miller on your hands.  However if they say:  "it felt awful, it felt like I was barely hanging on to each turn." then try a different approach and ask them::  "why do you think it felt that way?"  Look for information from them, that could give you insight on how to help them make the skiing feel more efficient.  Stance is a tricky issue, where and how people feel balanced is personal.  What works for one skier will not work for another, because people have different body types.  If you work from the athlete's perspective and coach them based on feedback you receive from them, you will never risk over-coaching.