F.M. Alexander (1869 - 1955) worked out the principles of the "Alexander Technique" over the course of many years. He always insisted that "anyone can do what I did if they will do what I did" but, as far anyone knows, no one else has ever managed that.
If you read an account of how Alexander worked out these principles, you will almost certainly realise straight away that it will be quite extraordinarily onerous, and take you many years of highly dedicated work to achieve this, and that even then you will most likely fail (for why that is, see below).
What Alexander came to realise, when he started trying to teach his Technique to others, was that the only effective way to communicate the principles to his students was to guide them to a practical experience of these principles in action, and that the only effective way to achieve this was to give them a new (non-habitual) experience by guiding them through movement in a new (non-habitual) way, so that they would gradually come to understand how it all worked.
I think it is quite unlikely that people with errors of co-ordination and posture will be able to learn the AT from a book or through online lessons with a teacher, with the possible exception those who have a strong natural aptitude for the principles and have already had a good number of individual lessons. In my experience it is much more likely that most students will actually make matters worse by attempting to learn the AT in this way.
This is for two main reasons:
Firstly, when our co-ordination goes wrong, we are not actually doing what we think we are doing. Our senses have become unreliable so that the 'wrong' thing has come to feel 'right' and, because of this, the 'right' thing can at first feel quite wrong.
Secondly, most of us attempt to resolve our problems by endeavouring to do what we imagine to be the 'right' thing. Not only may we be mistaken about what is 'right' (see previous paragraph) but, even if not, this approach is exactly the opposite of the method of the AT. In AT lessons, the student learns to become aware of the 'wrong' thing that they are doing so that, by ceasing to do this 'wrong' thing (through change of intention alone), the 'right' thing is free to happen, spontaneously, and by itself.
Because these two principles are at first so counterintuitive to most people, in practice almost everyone requires skilled individual assistance to learn the AT.
It is true that there are some teachers who claim to be able to teach the AT virtually, and I cannot state with absolute certainty that they cannot. I do accept that it is possible to impart some theoretical information in this way and to teach the semi-supine procedure, as would also be available online or in a good book, but a practical understanding of the principles is very hard to communicate to most people without hands-on teaching. In addition, there is no scientific evidence to support virtual teaching (as far as I know, every one of the studies on the effectiveness of the AT have been conducted with hands-on work) and the great majority of AT teachers reject this idea for the reasons set out above.
If you are interested in learning the A.T. this is my advice: find yourself a properly qualified teacher and go for an individual lesson. If that is not available to you because of the current situation with Covid-19, my best advice is that you practice the semi-supine procedure, which may be of some benefit (there are many good articles, videos and audios freely available online) and wait until the "lock down" is over to begin or to resume your lessons.
Peter Bloch 10/4/20