Read the title. Define every word in the title; look up any unknown words. Think about what the title promises for the book. Look at the table of contents. This is your “menu” for the book. What can you tell about its contents and structure from the TOC?
Read a book from the outside in. Read the foreword and introduction (if an article, read the first paragraph or two). Read the conclusion or epilogue if there is one (if an article, read the last one or two paragraphs). After all this, ask yourself what the author’s thesis might be. How has the argument been structured?
Read chapters from the outside in. Quickly read the first and last paragraph of each chapter. After doing this and taking the step outlined above, you should have a good idea of the book’s major themes and arguments.
You are now finally ready to read in earnest. Don’t read a history book as if you were reading a novel for light pleasure reading. Read through the chapters actively, taking cues as to which paragraphs are most important from their topic sentences. (Good topic sentences tell you what the paragraph is about.) Not every sentence and paragraph is as important as every other. It is up to you to judge, based on what you know so far about the book’s themes and arguments. If you can, highlight passages that seem to be especially relevant.
Take notes: Many students attempt to take comprehensive notes on the content of a book or article. I advise against this. I suggest that you record your thoughts about the reading rather than simply the details and contents of the reader. What surprised you? What seemed particularly insightful? What seems suspect? What reinforces or counters points made in other readings? This kind of note taking will keep your reading active, and actually will help you remember the contents of the piece better than otherwise.