QUESTION: How do you decide which book to take into your hands, and which book to stop reading if it goes too far, and how do you detach yourself from the content of it?
ANSWER: One of the important things I've learned about is the existance of "Divine Institutions", a social order of authority that God has set up for mankind. There are four of them and they are, 1) the sanctity of each person's individual volition in choosing things in life, 2) marriage (with the man in authority over the woman), 3) family (parents in authority over the children) and 4) nationalism (which includes military activity, which the Bible sanctions. Another huge subject). These institutions are not just for Christians but for everyone, and many unbelievers abide by them. Particularly in times past.
Many so-called "secular" books uphold these principles as they tell their stories. The Hornblower series comes to mind in this regard. Honor, courage, self-sacrifice and true principles of leadership and chain of command abound. As well as many other elements, including some analogies to Christ that I doubt the writer intended, but that I've found very illuminating.
Generally secular books portray people as they are without a relationship with Christ. Personally I'm not interested in reading about too much of this without the establishment principles -- I don't care for books that follow a person as he sins and sins and sins and that's the end. I want books that end well, where the characters learn something valuable and true, because the truth is, we who have a relationship with God through Christ do have a good ending ahead of us. Another truth is that people who live by the divine institutions as unbelievers will be blessed. I like books where justice and good prevail, because in the end they do. I can usually tell from the synopsis of the book or a review where it's going, and make my decision about reading a book accordingly.
As for how do I detach myself from the content, usually I don't do it very well. Which is one reason why I try to stop reading before I get far enough into it that I'm going to have a problem. And also another support for daily study of God's word. It helps to break the influence some books' worldly and evil contents might have gained over my thinking.