What I do when I'm going to read a book about a specific person or era in history is to read a quick abridged version of it like a Wikipedia page. Then if your interest in the subject is piqued, it should be easy to breeze through the book. Problem is that most of those books are written by professors, and it seems that their top priority is to impress their colleagues rather than provide an enjoyable learning experience for their readers. It can get annoying listening to or reading shit from pedants.
Management, strategy, and how-to guides I approach differently. I try to apply what I'm reading as I'm reading it to my business or personal life. If you find that some areas of management or business strategy is not applicable to you yet, create a company in your head with the problems that the solutions in the book deal with. This also helps tremendously in memorizing the material in the book, because you're associating it with a personal situation/problem, real or imagined. Also, you can jump around the book to find parts that are more interesting to you. You will probably go back and read what you skipped if you find the information later in the book to be valuable.
Management, strategy, and how-to guides I approach differently. I try to apply what I'm reading as I'm reading it to my business or personal life. If you find that some areas of management or business strategy is not applicable to you yet, create a company in your head with the problems that the solutions in the book deal with. This also helps tremendously in memorizing the material in the book, because you're associating it with a personal situation/problem, real or imagined. Also, you can jump around the book to find parts that are more interesting to you. You will probably go back and read what you skipped if you find the information later in the book to be valuable.