From the chapter "The Observing Self" in Charlotte Joko Beck's Everyday Zen:
There are several ways to practice. One is with sheer concentration (very common in Zen centers), in which we take a koan and push hard to break through. In this approach what we are really doing is pushing the false thought and emotion into hiding. Since they are not real, we suppose that it is OK to push them out of the way. And it's true that if we are very persistent and push on a koan long enough, we can sometimes break through temporarily to the wonder of a life that is free of ego. Another way, which is our practice here, is slowly to open ourselves to the wonder of what life is by meticulous attention to the anatomy of the present moment. Slowly, slowly we become more sophisticated and knowledgeable, so that (for example) we may know that when we dislike a person, the left corner of our mouth pulls down. In this approach everything in our life —the good and bad events, our excitement, our depression, our disappointment, our irritability — becomes grist for the mill. It's not that we seek out the struggles and problems; but a mature student almost welcomes them, because we gradually learn from experience that as this anatomy becomes clear, the freedom and compassion increase.
A third way of practice (which I view as poor) is to substitute a positive for a negative thought. For example: if we are angry we may substitute a loving thought. Now this changed conditioning may make us feel better. But it doesn't stand up well to the pressures of life. And to substitute one conditioning for another is to miss the point of practice. The point is not that a positive emotion is better than a negative one, but that all thoughts and emotions are impermanent, changing, or (in Buddhist terms) empty. They have no reality whatsoever. Our only freedom is in knowing, from years of observation and experiencing, that all personally centered thoughts and emotions (and the actions born of them) are empty. They are empty; but if they are not seen as empty they can be harmful. When we realize this we can abandon them. When we do, very naturally we enter the space of wonder.
This space of wonder — entering into heaven — opens when we are no longer caught up in ourselves: when no longer "It is I," but "It is Thou." I am all things when there is no barrier. This is the life of compassion, and none of us lives such a life all the time. In the eye-gazing practice, in which we meditate while facing another person, when we can put aside our personal emotions and truly look into another's eyes, we see the space of no-self. We see the wonder, and we see that this person is ourselves. This is marvelously healing, particularly for people in relationships who aren't getting along. We see for a second what another person is: they are no-self, as we are no-self, and we are both the wonder.