May Christians read self improvement books? We know the best Book we have is the Bible, which has everything for life that we need to live a perfect life. I would like to know should we stop with Bible and Books that are based on Bible, or may Christians read non-Bible based books that teach good things such as "The Power of positive thinking" etc. They seems harmless written by well known authors like Dale Carnegie, Norman Vincent Peale etc.
This is opinion only, but I'll throw my two cents in.  I'm also not going to add in supporting Bible verses as I'll stick to commonly accepted, cross-denominational concepts that any Christian should be familiar with.  (If comments ask for verses, I will come back and edit them in.)



Most of the self-help books that I've read personally are, in retrospect, based on very humanistic concepts, or the popular psychology of the day.    However, many of them contain very good ideas mixed in with the psychobabble.

My personal opinion is that there is nothing inherently wrong with reading self-help books, provided that you've got a solid foundation in Biblical doctrine, and are able to discern the good from the concepts that are anti-Biblical.  

Many of these books have value, and follow along with Christian teachings.  Books on success often advocate following the golden rule - treating your peers, employees, customers, etc, as you'd like to be treated.  Or the teach the value of honesty, integrity, etc.  None of these are anti-Christian, and all are examples of how God would have us behave anyway.

The biggest pitfall that I an see with these books is that they can further the illusion among the unsaved that following the advice in the books makes them a "good person".  Of course, a person has to realize that he or she is lost before they can turn to the Savior for salvation.  We can all be better people, but we can never be good enough to earn our own salvation.  (If we could, the Cross would not have been necessary.)

Then there are the books that teach outright contradictions to the word of God.  Humanistic, or spiritual growth books that point to one new age theology or another.  Again, these can be dangerous for obvious reasons.  However, I still believe that someone with a grounding in doctrine with the gift of discernment can still read these books and use the knowledge for God's will. the people who fall for these lies need the Savior just as much as anyone else, and you can't refute something you don't know about.  

As a parallel to this last once, many Christians study the beliefs of various cults and non-Christian religions in order to learn how to more effectively witness to those involved.  It helps to provide a common starting point.  Being aware of what's being taught in these "new-agey" books can be valuable for the same purpose.

The bottom line comes down to whether or not you're grounded enough in the Word to understand and discern the truth from the lie.