[1] Barbara Minto - The Pyramid Principle
Please note that there has been criticism raised in recent years about the pyramid principle. Some argue that it turns people's writing in "McKinsey" style, which could be even more confusing to the audience. For instance, Duff McDonald writes in his book, "The Firm", the details on Barbara Minto's text, "The Pyramid Principle". He offers a useful critique of writing things in that style.
Minto's book is useful to read, but just be aware of the criticism raised. This will help when you're thinking about your audience and hoping to explain things to them.