The old saying says, "You can't judge a book by its cover." That axiom will serve you well in many arenas, but when it comes to books, newpaper articles, even Christian materials you must develop skills to do just that. So, below are some of the conscious things I do to categorize a book before I decide whether or not to invest my time into it.
First, assuming the title appeals to me, I pick up the book and read either the inside flap of the dustcover or the back cover to get a synopsis of what the book is about.
Then, I look at the publisher to see if it is one that is familiar, or noted for being conservative, liberal, Calvinist or Armenian, Pentecostal or non, Evangelical, etc.
Then, I will investigate the author to see if I recognize him or her, and in order to discover what school of thought he or she may represent. In particular, I want to know whether the author is reformed or not (Calvinist or Armenian); Pentecostal or not (if not Pentecostal, are they hostile to Pentecostalism?); Emerging church or traditional; evangelical or mainline; what is his or her denominational affiliation, what schools did he or she graduated from, his or her age, etc.).
The date of a publication can be important as well. If a book speaks to our culture or current events, but was written prior to 9/11, I will not likely be interested. The world has changed drastically since that time and I want to know that the author is aware of those things.
After all of the above, if still interested in the book, I will look at the Table of Contents to see if I can discern anything more about the writer's bias's, but, of course, also to see if the book is going to be very interesting.
You may ask, "Why go to such trouble? Are you being judgmental?" It's not about being judgmental, it's about choosing who gets to influence my thinking. The above criterion may not necessarily rule out the book, but it will help me to process the information.
For example, if an author is non-Pentecostal, perhaps even hostile to Pentecostalism, I will think twice about hearing what he or she has to say about spiritual gifts knowing that the author probably believes that many of the so called "sign gifts" of 1 Corinthians 12 are no longer available. I also won't be too interested in what a non-Pentecostal will tell me about worship because, by and large, a non-Pentecostal is not open to the interruption and redirection of the Holy Spirit in the midst of a worship service. If the writer is not open to the Baptism in the Holy Spirit, in my assessment, he or she has missed a significant aspect of spiritual maturity, depth, and insight. There, I said it.
This approach to a source of information is consistent with the concept of critical reflection. Critical reflection takes an honest look at information and those providing it and ultimately makes a decision about which part of the information to keep and which part to disregard. But BEWARE! Critical reflection can be a dangerous business unless one is equipped to process challenges to what he or she believes. All the more reason to "pick your battles" as they say, and be particular about opening up your faith, knowledge, or beliefs to question or assault.
One final word: Just because you hear someone preach a sermon on the radio or television or Youtube, or just because someone writes a book, does not mean it is gospel truth. EVERYTHING must be tested through the filter of Scripture.