The other day I was asked: "David, how did you learn Astral projection?" A straightforward enough question; but after I has answered it, Benjamin suggested that what I said would interest others too.
I learned how to travel in the Higher Worlds by being taught by others who could do so. Over the past 30 years, I have only come across a handful of individuals who learnt Astral travel from reading a book. But, I have known several hundred people who learnt conscious Astral travel by esoteric teachers.
Of course, we all have the ability for Astral travel, in the same way that we all have the potential to be able to swim. Nevertheless, for best results we need a living mentor. I would not want to take driving lessons from someone who could not drive!
My astral training began with short journeys out-of-body in the company of my tutor. This then progressed to journeying - with my mentor - to various Astral temples, colleges of wisdom, and healing sanctuaries. I was also taught how to strengthen my Subtle body (rather like an "astral workout"), so that I could prolong my Astral Plane journeys. After various tests in proficiency, I was deemed ready for Group astral work. In the company of similarly trained people, we would (and still do) undertake missions of Mercy, in the service of the Lords of Light.