Find a position in which you can comfortable remain for ten minutes with your back straight but not rigid. This time, instead of picking an object of focus such as the breath, just observe thought itself. Simply let things happen as they do. Just watch. Be aware, as thoughts arise, that the thoughts are there, without gettting involved in the content of the thoughts. Let all images, thoughts and sensations arise and pass away without being bothered, without reacting, without judging, without clinging, without identifying with them. Just keep letting go of one thing after another.
The thoughts that arise are not obstacles or hindrances. They are just the objects of our observation. Keep the mind sharply aware, moment to moment, of what is happening, what the mind is attending to. If you feel tense from trying to watch your mind, relax. The sky doesn't get all tense trying to see the clouds. Everything is just as it is.
Keep in mind the idea of letting go. As thoughts or sensations, images, memories, whatever, rise into your awareness, notice them, witness them, and then let them go. Keep letting go again and again. And of course, once you are really comfortable and at home in pure awareness, then you can let go of the thought of letting go as well.
(Ram Dass, How Can I Help, 1985, pp. 102-103)
Here's a version of Letting Go you can download: