The first thing the Buddha did after leaving his home was to seek out teachers. He sought out Alara Kalama and Uddaka Ramaputta
""Having thus gone forth in search of what might be skillful, seeking the unexcelled state of sublime peace, I went to Alara Kalama and, on arrival, said to him: 'Friend Kalama, I want to practice in this doctrine & discipline.'
"When this was said, he replied to me, 'You may stay here, my friend. This doctrine is such that a wise person can soon enter & dwell in his own teacher's knowledge, having realized it for himself through direct knowledge.'
"It was not long before I quickly learned the doctrine. As far as mere lip-reciting & repetition, I could speak the words of knowledge, the words of the elders, and I could affirm that I knew & saw — I, along with others.
"I thought: 'It isn't through mere conviction alone that Alara Kalama declares, "I have entered & dwell in this Dhamma, having realized it for myself through direct knowledge." Certainly he dwells knowing & seeing this Dhamma.' So I went to him and said, 'To what extent do you declare that you have entered & dwell in this Dhamma?' When this was said, he declared the dimension of nothingness."
So, perhaps for all of the books and CD's out there, a person can maybe attest to knowing the teachings of these items by mere lip-reciting and repetition. But Alara Kalama invites the Bodhisattva to "stay", since a person staying under the direction of the teaching and the teacher can, if he is wise enough, know that same teacher's knowledge, having realized it for himself through direct knowledge.
As far as the question goes as to who should become the prime teacher of the dharma after the Buddha passed, it wasn't about who was going to teach, it was about who was going to lead the sangha. The answer was, to Devadatta, that no one at all, not even Sariputra or Maha Moggallana, would lead the sangha. Teaching must have continued though, as best as it could be done without the Buddha there.
You can, if you really want to, teach your self Yoga. And in the same way you can teach your self proper meditation. But if you set out to teach your self yoga, and the same kind of posturing that the traditional yoga practitioners manage to practice, this will take you a very, very long time.
There is just one principle in Yoga. Focus on the one part of the body. If you are patient and focused you will let yourself fall into the posture. It happens naturally. I'm teaching my self Yoga in various stages, even as I write this. So far, by my self, all on my own, I have found out how to spontaneously and without pretentious assumption, get into that posture where you Namaste with your hands to your heart (or above your head) and bring your right leg up and bend it so that your heel sits above or upon your left knee. Whatever this posture is called, I have -all by my self, learned how to find my self in it. I am very proud, because I already knew this was a Yoga posture and in a very specific way I learned to naturally fall into it. It's a heart posture.
As for the other hundreds of other poses; those will most likely have to wait. To be honest there isn't so much as one percent chance in three million that I will ever arrive at anything beyond four or five postures based on my own investigation.
I believe that attention to ones breath is beneficial in any circumstance. It can be beneficial to every aspect of a person's life, regardless of what situation they find themselves in. At work, with family, paying attention to ones breath actually makes life a lot simpler. It makes decisions easier and actions or words more beneficial for all. You are breathing all of the time anyhow. One might as well learn for themselves what happens to their natural behaviors when that breathing process is given over to mindfulness. It turns out that what you want to do, you do better, you do without hesitation, you do without doubt, you do against all laziness.
So, since most people have to go through the mundane routines of daily life anyway, they should do their selves a favor and pay mind to their breath. Chores become something you're just doing when you pay mind to your breath. Like, just the other day, I learned that even though I drive an automatic vehicle, the gears are shifting as if I was driving a standard. Whereas in the past when I used to accelerate I would step on the accelerator with one steady uniform amount of pressure, now -having stopped all thinking about the car, instead focusing on the driver and his breath (that's me), I realized that I can extend the life of my car by driving it as if it were a standard shift vehicle.
This example shows that when I lacked focus on my self I failed to understand the nature of the vehicle surrounding me. However, by simply paying attention to the most basic of things; breathing, I gainfully learned or rather became sensitive to something I should have known for a long time, e.g. that even an automatic transition needs time away from the accelerator in order to properly transition. Now I don't drive quite so much like the moron I used to. It's simple things like this that are so easy to forget about when we go about life pretending that our existence is somehow involved with the objects in our lives.
So, I like how my life works when all I do is think about my breath, because I get things done and I avoid situations and events which would otherwise make me uneasy, anxious, doubtful. And that's just as attention to breath applies to the mundane life I live.
If I was to apply this attention to my breath for the purpose of setting my mind free of all imaginable attachments I wouldn't be conducting my life as it applies to the outside world, I would be attempting to conduct my life as it applies to the most elemental form of my existence. In that case, I would seek advise for the proper use of such a technique.
'The currents in the world that flow, Ajita,'
said the Blessed One,
'Are stemmed by means of mindfulness;
Restraint of currents I proclaim,
By understanding they are dammed' (Sn.1035)