Nordic Skiing, and Student Tips for Skiing Long!

Apply many thin layers of wax, not 2 or 3 thick ones

At the start of a race don't start too fast, or you will run out of gas fast if you do
Don't attack the hills unless you have trained to do that.  Slower
easier ascent helps keep energy reserves for later
Try to stay up with someone a little faster than you.

Don't overdress. Start a little chilly and you will warm up fast.

Learn to always be looking ahead at the trail, to decide what technique is required for the terrain

Try to transition smoothly from double pole, to single kick double pole, to diagonal stride and visa-versa.

The hippity-hop, comes in handy going around corners, in order to maintain momentum, especially when there is a hill to climb around the corner.
Bring kick wax with you on long ski runs. There was no wax left on the skis after the ski race.

Put base binder on in 2 very thin layers, iron in, and be sure that it does not come through, when waxing in the kick layers.

Be sure to examine and determine where is the wax pocket after a long ski or race. ONLY your skis will tell you, with your technique, where the wax pocket really is. The wax pocket will change depending if you have gained weight, wearing a pack, or you now have better technique. 

Do a better job of waxing in the first place.

Try not to snow plow as much, but do step or skate turns instead. That way the wax will not wear off as quickly.

Remembered to determine where the fastest snow is on any part of the track.

Do lots of double poling wherever you can, as long as you are going at least at the same speed as the next person.

Dates and almonds do not freeze in the cold.
Not a good idea to ski long with a hangover.

It only takes around 15 seconds to switch your skis left to right, etc.

It takes about 2-3 minutes to slap on a couple of layers of wax, which may still be of much benefit, if there is a while before the long ski or race is over.