@dschuetz's answer is pretty good. I would add that it helps to hang around people who are themselves critical thinkers. Not the negative cynical kind, mind yo

@dschuetz's answer is pretty good. I would add that it helps to hang around people who are themselves critical thinkers. Not the negative cynical kind, mind you, but those who like to explore new ideas, question old ones, and are not afraid to admit that some new ideas ended up sucking (after some consideration) and that the old ones weren't too bad with which to begin. Surrounding yourself with people like these help expand perspective and avoid group think.