Although they don’t emphasise the point until near the end of their book, Adler and van Doren don’t advocate you should follow their advice for every single book you read; it’s really intended to help you get the most from difficult-to-read, primarily academic books.
There’s plenty of sound advice in here about familiarising yourself with the book you’re about to read, identifying its main theses, and its key sections, before engaging with it in detail. The authors suggest you underline key passage and make marginal annotations—something this reader will never be able to bring himself to do. I guess I’ll just have to stick with my trusty index-card bookmarks.
Adler and van Doren also advocate plenty of summarising and other note-taking. Later on, they explain how to assess whether books’ authors seem to know what they’re talking about, and explain when it is—and when it is not—reasonable to reject an author’s theses. There is also some good advice about syntopic reading: reading several different authors on the similar and related topics.
As I say, How to Read a Book contains plenty of sound advice. My only reservation is the authors do go on a bit at times, repeating points they’ve already made more than once, and recapitulating stuff they’ve only just said. This is a long book, which could easily have been reduced to one-third the length without losing any of the key ideas. Such editing would surely have made the book even more useful.