Al Mohler has some good thoughts on reading books. Here are the main points, but go read the whole thing.
1. Maintain regular reading projects. I strategize my reading in six main categories: Theology, Biblical Studies, Church Life, History, Cultural Studies, and Literature. I have some project from each of these categories going at all times. I collect and gather books for each project, and read them over a determined period of time. This helps to discipline my reading, and also keeps me working across several disciplines.
2. Work through major sections of Scripture. I am just completing an expository series, preaching verse by verse through the book of Romans. I have preached and taught several books of the Bible in recent years, and I plan my reading to stay ahead. I am turning next to Matthew, so I am gathering and reading ahead -- not yet planning specific messages, but reading to gain as much as possible from worthy works on the first gospel. I am constantly reading works in biblical theology as well as exegetical studies.
3. Read all the titles written by some authors. Choose carefully here, but identify some authors whose books demand your attention. Read all they have written and watch their minds at work and their thought in development. No author can complete his thoughts in one book, no matter how large.
4. Get some big sets and read them through. Yes, invest in the works of Martin Luther, Jonathan Edwards, and others. Set a project for yourself to read through the entire set, and give yourself time. You will be surprised how far you will get in less time than you think.
5. Allow yourself some fun reading, and learn how to enjoy reading by reading enjoyable books. I like books across the fields of literature, but I really love to read historical biographies and historical works in general. In addition, I really enjoy quality fiction and worthy works of literature. As a boy, I probably discovered my love for reading in these categories of books. I allow some time each day, when possible, to such reading. It doesn't have to be much. Stay in touch with the thrill.
6. Write in your books; mark them up and make them yours. Books are to be read and used, not collected and coddled. [Make an exception here for those rare antiquarian books that are treasured for their antiquity. Mark not thy pen on the ancient page, and highlight not upon the manuscript.] Invent your own system or borrow from another, but learn to have a conversation with the book, pen in hand.