How to Skate-Ski: a tip or two
The most common error in XC ski-skating is to use what's called the "toilet seat" posture. This is how people ski who are being uncommitted and hesitant on their skis.
The corollary in alpine skiing is "the back seat"---that's where you go when you're bump-skiing and you're about to be ejected. You want to stay in the driver's seat, out of the back seat. You lean forward into your boots and keep your hands forward.
Well, the same is true in XC.
Basically, all XC techniques use the same body position. (Skating is really not much different from classical. It's not even that much faster---skating is about 10% faster on the WC level. On medium-steep uphills I even find that classic is faster than skating.)
The desired body position is to have the body tilting forward. To flex deeply at the ankles. To have what my Norwegian technique video tape calls "good forward fall."
What you DON'T want is to ski with your torso upright, your arms reaching forward, and your butt drooping to the rear.
Now, these tips are for FAST skiing on groomed trails---that's where skating and fast classic happens. For classic TOURING it's fine to just toodle along however.
Here are a few tips for getting a good position for performance skiing:
1. (This first tip is from the USST.) Start from a stop at a small uphill. With your skis in a V position and weight on both feet, bend your knees and drop your butt back so your thighs burn. Now tilt forward at the ankles and drive your knees forward toward the tips of your skis. Your legs should stop burning and you should roll forward up the hill. Part two: without applying energy to the kick begin to shift your weight from ski to ski maintaining this forward, low position---just use your falling momentum to go forward.
2. A great way to get "forward fall" is to pole properly. (Well, you can't get it without proper poling.) A great test of correct poling is if you missed your pole plant you'd fall on your face. So the right way is to throw your body forward and catch yourself with your poles. The correct posture is to have your back in something like a C-shape. Round out the lower back and hump the upper back, roll shoulders forward. This lets you initiate poling with your *ABS*. A crunch starts the poling, with the help of your falling torso weight. What helps this is if you slightly flare your elbows. Elbows point to the sides a bit. It probably also helps to keep your chin down---that's most relaxed and works best with slumped shoulders, lift eyes to see down trail.
3. Again, think of pressing knee to ski tip to help you flex the ankle (this is just a simpler version of Tip 1).
4. For going up STEEP uphills you don't have to pole all the way thru or kick all the way out---that takes too long and you bog down and you might drift back to the toilet seat. Just hit the initial 'sweet spots'---it's like the catch of a canoe-paddle or rowing oar stroke---that first 'pop' is the most effective. Get a good crunch to start the poling, get good initial kick and weight transfer, and that's all you need. Try to have quick, light feet. Basically, a half a stroke is all you need for the steeps. It's like you're scampering up.