Quite honestly, it needs to be short and to the point. I love books, but these days I use them more as a proven, go-to source of quick reference.
When it comes to educating myself, I feel that online courses and workshops are the best way to do so. Even entire tracks can be consumed in small amounts, and each section ends with a review/quiz. TED talks and conferences can be interesting as well.
Technology today, imo, should be properly summarized and not buried in detail since it evolves quicker than the proper time we'll need to digest it, and by the time we do, part of what we learn will be antiquated. It's why I feel this industry is currently biting off more than it can chew, at the moment.
The last book I devoured was "Refactoring: Improving the Design of Existing Code" - and it was easily done in bits and pieces over a month or so. Now, I occasionally go back into it for reference, and re-read something I need to understand better.
Being, at least partially, familiar with the material also helps to dictate how much you'll understand about it during the learning process. If it's unknown territory, don't take on the challenge unless you're planning to dedicate the time needed to educate yourself correctly - which often requires continuously deep diving into other related topics, as well.