Reading well is a skill, and it requires practice.
I've spent much of the last week thinking both about both the books I've read and the process of reading. In that time, I've read books ranging from Truth and Trolls to Stephen Hawking's A Brief History of Time and from The Shadow Rising (a fantasy novel) to Billy Graham's Angels. There's a lot of good material in every book I've read, but there's been a lot of bad material mixed in. Sorting it out requires attentive thought. I thought I might share some of my approach, in the hope that it'll help others. The following list is hardly comprehensive - and I'd love to hear any thoughts or suggestions, as well as references to similar lists! In no particular order (except for the first and last):
Nearly every book you will ever read has something you can learn. There may be a few exceptions out there, but I've yet to find one, and I've read some absolute duds - the sort that should never have made it to an editor's desk, much less off of it. The trick is recognizing which parts of the book you should walk away with. Our basic assumption should be that we can learn something from the book, so we should also be asking what as we read. That will look different with fiction than with nonfiction, of course, but it's applicable to either.
Read humbly. Don't think you know everything. You won't learn much otherwise. That means depending on the Holy Spirit to teach, no matter what you read. (This is a big one for me, and one that I'm learning a lot about right now. Human judgments are quick to err without His help.)
Deciding what to take away from any book requires thought. The amount of thought may vary, but there will be some no matter what. We have to decide what is valuable, what is not, and what is merely neutral. In some ways, the question is the hardest for the best and worst books. In the worst, the temptation is to simply dismiss everything the author says: when so much is obviously wrong, it's easy to think that everything is, but that's not necessarily true. The challenge with the best books is precisely the opposite: to carefully decide what is not good when so much is. No author's words are gospel. All books - good and bad, well-written and poorly alike - must be tested against Scripture.
Sometimes we learn negatives rather than positives: don't do this, avoid that, this is heresy and worth refuting. Even if that's all, you've still learned from what you've read. It wasn't necessarily a waste of time. (That being said, I don't advocate spending most of your time reading heresy!)
On that note, think about how you spend your time. You don't have much, so spend it carefully. Make good use of breaks and vacations.
Read widely. Don't limit yourself to one genre, or even one overarching category. Lovers of fiction, make yourself read some good non-fiction - and you non-fiction purists, make a point to pick up a novel on a regular basis. Our imaginations and our intellects both need training and sanctifying. Read yesterday's best-sellers as much (or more!) than today's - don't fall prey to temporal arrogance. Read old novels and new ones, church fathers alongside the current preachers. Two applications of this: I'd like to read more short stories, since basically all of my fiction reading has always been novels, and I want to start reading the church fathers at length.
Read with pleasure. Don't make yourself trudge through book after book you can't stand. There are certainly times when we should read books we don't particularly enjoy; it is good to challenge ourselves and expand our boundaries (see above). But reading should also be a source of joy and delight. Light, "popcorn" reading is sometimes a great help here, and I make a point to sprinkle light-hearted fiction in amongst my diet of Dostoevsky, Piper. etc. As much as I enjoy the heavy hitters, they can become tiring after a while. A good dose of Robert Jordan from time to time helps reinvigorate my desire to read harder things, as well as being fun in its own right.
Form and content don't always match up perfectly. I've read well-written books full of heresy and doctrinally sound books that should have been rewritten from scratch. I've read novels with well-written characters but terrible worldviews, and vice versa. (I'm sad to say I've found more Christian novels in the "good worldview, bad writing" category than not. If someone knows of any really good modern Christian novelists, I'd love to hear about them.) If we're going to be good readers, we need to be able to recognize the good parts of bad books, and vice versa. If the prose is bland but the story compelling, learn from the narrative and leave the prose behind. If the form is fantastic but the content heretical, recognize both for what they are. (This is another good place to practice discernment in how we spend our time.)
Read Christologically. Whether novel or theological treatise, whether Christian or pagan, look for the marks that God has left on the human heart. Look for Him in books on marriage and in mystery novels. Look for Him, and if you do not find Him, then you have real reason to criticize. You may be pleasantly surprised to find Him where you did not expect, though you may also be sad not to find Him where you did expect.