A few years ago at a party, I asked a member of the Judge Advocate General corps jokingly about how many ways he knew how to say things in Latin. And he replied seriously, that a good lawyer does not try to say things in a complicated way. All a good lawyer does is say what you can do, and what you can't do. He added that sometimes a really good lawyer can find ways to do things that you normally couldn't do, but the basics of it are, all the expertise of being a lawyer boils down to knowing what is a good idea and what is not.
The reason I mention this is that the most important wilderness survival skill, from my experience, is simply to know what you can do and what you can not do. This is actually an important thing to remember, because much of the more romantic and popular views of wilderness survival depict the employment of exotic skills. Very rarely will a situation of being lost in the wilderness involve weaving together rushes to form a lasso to capture a passing grizzly bear, which you will then ride into civilization. Very rarely will you even be doing something like eating bugs or drinking your own urine. For the most part, if you are at the point of doing these things, you are probably already well on the way to death's door.
The most important wilderness skills are to know how far and how fast you can walk, what temperature you can endure and for how long before undergoing hypothermia, how much water you need to drink, how much food you need to eat, and a few other basic questions. Then, remember that situations can change these answers, and that they will often change many of them at once. (For example: as you move across rough terrain, the speed you walk will go down. This means it will take more time, and you will need more water, and are also at more risk of hypothermia.) Once you know what you can do, make it part of your plans, and stick to it. Resist the temptation to mentally exaggerate what you can do ("20 miles in a night...that is possible"), and resist the temptation to say "Just this once, lets go a little further".
Unlike other skills, the skills of surviving in the wilderness are neither exotic or technical. They are rather a fairly simple set of questions about realistically knowing your limitations. The hard part of these skills is often to be honest with yourself, and to hold fast to these rules.