These shelters are quick to prepare: simply dig down to the ground, place some spruce in the bottom and along the sides (scrub birch can do in a pinch), place your pad and sleeping bag in there and let Morpheus take you away. But do look up: there are few sights more impressive than the northern lights, against a backdrop of the Milky Way.
If the weather is less than ideal you should make a roof for your trench. This can be anything from a parka held up by your skies, a poncho or ground sheet, or a set of snow blocks. Talking of snow: don't place the "leftover" snow too close to the edge of the trench, or it will tend to roll down onto you during the night.
For better shelter you should build a quinchie. This is a grown up version of the snow caves you built as a child. Start by piling up a big pile of snow (at least as tall as you are, and at least a couple of meters in diameter. Pack the snow down a bit as you go, with a ski, your shovel or whatever. Let this stand until it has hardened (anything from less than half an hour to several hours).
Place short sticks (30cm or so) all over the surface of the quinchie, such that you
will know when you approach the surface when excavating (this step can
of course be performed before the snow has hardened).
Start excavating by making the smallest necessary opening, and hollow out the shell. Make sure you have a flat surface to sleep on, and enough headroom so that you can sit up without touching the ceiling. Make a good sized ventilation hole, and your home is done.
A few hints:
Under normal conditions firewood must be dry to burn. This is not the case under arctic winter conditions. The shrub birch will burn regardless once you've gotten the fire going.
And remember that if you build your fire on the snow said snow will melt. It is hard to keep a fire going in a puddle!
Dehydration is an important danger in the cold, and you should drink as much as 5-7 liters of water each day. This is a lot of snow to melt, but it helps you fighting the cold. Make most of this water spruce needle tea (if you have spruce...), since the vitamin C helps you as well when it comes to fighting frostbite.
It is easy to loose things in 1,5 meters of snow. Get into the habit of never, ever placing anything smaller than a ski pole on the snow without having it attached to something else. If you don't use it, put it away.
This should not come as a surprise to anyone of you, but think about is again. If your clothes are covered in snow some of it will melt on your clothes. There it will melt, only to later re-freeze. Ice conducts cold, in addition to making your clothes stiff and heavy.
The solution is a snow brush, either a cut-off dishwashing brush (perhaps with a cord on it to prevent lossage), or an improvised one made from some twigs. Whichever kind you have: use it.