I was able to answer the book's title question within a couple of minutes' reading! A practical book which helps identify negative, unhelpful patterns of speaking, and how this impacts on your life, mindset, health, etc. I would reccommend it, and have lent it to two family members already.
Charles Capps is another great teacher on this subject, but goes a step further with insightful, down-to-earth explanations. I found his brief teaching on 'calling things as though they were' a revelation - having never 'got it' before - having been a Christian for many a year.