About ten years ago I heard Ben Patterson, campus pastor of Westmont College, say something that I will never forget. Ben told the story of a retired pastor who began noticing that his former congregation was sliding away from orthodoxy. The pastor saw this as his fault, noting the one thing he thought he did most poorly as a pastor. The pastor stated, in two sentences, his great failure as a pastor:
I always told people what to believe.
My great mistake is that I never told my people what NOT to believe.
From Between Two Worlds
Here's a book to start with what NOT to believe.