As you sit with a good posture, you pay attention to your breath. When you breathe, you are utterly there, properly there. You go out with the out-breath, your breath dissolves, and then the in-breath happens naturally. Then you go out again. So there is a constant going out with the out-breath. As you breathe out, you dissolve, you diffuse. Then your in-breath occurs naturally; you don't have to follow it in. You simply come back to your posture, and you are ready for another out-breath. Go out and dissolve: tshoo; then come back to your posture; then tshoo, and come back to your posture.
Then there will be an inevitable bing!—thought. At that point, you say, "thinking." You don't say it out loud; you say it mentally: "thinking." Labeling your thoughts gives you tremendous leverage to come back to your breath. When one thought takes you away completely from what you are actually doing—when you do not even realize that you are on the cushion, but in your mind you are in San Francisco or New York City—you say "thinking," and you bring yourself back to the breath.
It doesn't really matter what thoughts you have. In the sitting practice of meditation, whether you have monstrous thoughts or benevolent thoughts, all of them are regarded purely as thinking. They are neither virtuous nor sinful...No thought deserves a gold medal or a reprimand. Just label your thoughts "thinking," then go back to your breath. "Thinking," back to the breath; "thinking," back to the breath...