When it comes to outdoor skills, one should never stop learning. There is always something new learn or skill to refine. The knowledge to develop such skills can come from many places, but in this article I place them in three categories: people, books, and experience. There will often be overlap between them, and by using all three, you can become a highly skilled outdoorsman.
People
In the past, this has consisted of only one form: in person interactions, which is still the best form of learning from people. If you know someone with a great deal of outdoor experience, talk to them, ask them questions, get their opinions and views. Or better yet, go on an outdoor trip with them. This way, you can combine learning from people with learning from experience. One of the most common ways to learn outdoor skills from people is if your parents ever took you camping when you were a kid. Being taught something as simple as starting a fire by someone who has done it is a great way to learn.
In today's age of computers and internet connections, learning from people has taken on further forms. Youtube is full of all kinds of videos from people offering advice on any outdoor skill you can think of. Web forums offer places for people from all over the world to come together for discussion. Blogs (like the one you are reading right now) offer a way for those with knowledge and experience to share it.
One note about learning from people: it is often very effective, but it can be unreliable. Someone may want to teach you their favorite technique, even though it may be a poor one, or even if it is a good technique, there may be even better ones out there. One of my personal life mottoes applies here: just because something works doesn't mean it works well, and just because something works well doesn't mean there isn't something that works better.
Books
This could be considered another form of learning from people, but I have decided to list this in a separate category. Books are typically more formal, organized, and linear than learning directly from people.
My personal favorite source for books on outdoor skills is United States military field manuals. The military has invested a lot of money into making manuals on just about everything, and many of them have non military applications as well. They are completely free to download online, and you can print them out for yourself. Many field manuals can be found for sale online in print form as well. If you look up only one field manual, make it FM 3-05.70 - Survival (this manual, and all the others I mention, can easily be found with a simple Google search). This manual has basic information on just about every outdoor topic you can think of - starting a fire, basic first aid, building a shelter, gathering food and water, identifying edible plants, operating in hot environments, operating in cold environments, etc. There are also other manuals that give more detailed information on specific topics. Here are some that I recommend.
FM 3-97.6 - Mountain Operations
FM 31-70 - Cold Region Operations
FM 21-11 - First Aid for Soldiers
FM 21-26 - Map Reading and Land Navigation
There are also many other potentially useful field manuals out there. Field manuals do have some weaknesses though. The most obvious one is that they contain a lot of information that a typical outdoorsman has no need of. Subjects like "Survival Movement in Hostile Areas" are not needed by someone who is just camping. Fortunately, you can skip over the sections that are not applicable to you.
Books in general have the weakness of being bulky and heavy. They are fine for reading at home, but they are more difficult to actually take with you camping, especially if you are hiking or backpacking. The most obvious way to overcome this is to study everything in advance so that way you know it when you get outdoors. The problem with this is that you cannot remember everything and you really need something on hand for reference. Another option is an ebook reader like an Amazon Kindle or a Barnes and Noble Nook. These can digitally store thousands of books in a small package for easy reference later. But then you run into issues associated with all electronics, like battery life, durability, and general reliability issues.
My choice is to have several books that I read at home, then when I am actually outdoors, I carry a small pocket survival book that is lightweight and easy to carry. The one that I have is called SAS Survival Guide by John Wiseman. It contains a lot of valuable information, yet is small enough to carry in a pack without taking up too much space or weight.
Experience
Experience can be a rough way to learn, but it is also extremely effective. You generally do not want to rely on experience alone to develop you outdoor skills (i.e., running off into the woods without doing any studying about the skills needed to survive and expecting to learn them along the way). You want to combine actual experience with learning from people or books (or better yet, both). If you want to learn how to start a fire without matches or a lighter, read up on it first; then, go out and try it.
Be careful with learning from experience, as it also is the riskiest way to learn. Always go in armed with information and equipment and always have a backup plan. For example, bring some matches along just in case you can't get that fire started without them. When trying something the first time, it is usually best to over prepare. Bring more water, more food, more clothing, etc., than you think you may need. Likewise, try studying different ways of doing the same thing. As you are out in nature and you use your gear and try different techniques, you will learn what gear you really need and what techniques work the best for you.
There will also be times where you do learn something purely from experience, despite not having studied it beforehand. For example, I accidentally learned a trick when I left my boots outside my tent overnight. I left them in a spot where they were in direct sunlight in the morning, which made them warmer and more comfortable to put on in the morning than if I had left them somewhere shaded. Obviously, certain weather conditions may prompt me to put my boots in a more protected location, but when I think the weather will be fair, I always leave my boots out overnight in a location where they will be in direct sunlight in the morning.
Ultimately, experience is how you will really learn everything. Until you actually get out and do something, it is only theoretical knowledge; it does not become practical until you actually do it.
Conclusion
Learning about the outdoors is really a lifelong lesson; there is always something else to learn. The purpose of this article is to get you to consider the different sources of outdoor knowledge, to consult them, then to finally get out and do them. Whether you have never even been camping or if you are an experienced outdoorsman, keep learning and keep trying new things. Try a new fire starting technique, try using a tarp and paracord to make a shelter instead of using a tent, try foraging for food. The more you learn and expand your outdoor knowledge and experience, the more enjoyable and more safe your outdoor adventures will be.