In the past three years I think I've listened to the audio version of The Power of Now about 7 times. Here's a favorite quote of mine from Tolle's book:
Be present as the watcher of your mind -- of your thoughts and emotions as well as your reactions in various situations. Be at least as interested in your reactions as in the situation or person that causes you to react. Notice also how often your attention is in the past or future. Don't judge or analyze what you observe. Watch the thought, feel the emotion, observe the reaction. Don't make a personal problem out of them. You will then feel something more powerful than any of those things that you observe: the still, observing presence itself behind the content of your mind, the silent watcher.