One of the ways to approach the idea of mindfulness and one-mindfully is through learning to breathe mindfully, or conscious breathing. Our breathing goes on all the time, but mostly it's not conscious. We are not thinking about it.
Following is a meditation by the Buddhist monk Thich Nhat Hanh from his book, "Peace is Every Step." Marsha Linehan greatly respects Thich Nhat Hanh's work and quotes him in the DBT manual.
"There are a number of breathing techniques you can use to make life more enjoyable. The first exercise is very simple. As you breathe in, say to yourself, ‘Breathing in, I know that I am breathing in.’ And as you breathe out, say ‘Breathing out, I know that I am breathing out.’ Just that. You recognize your in-breath as an in-breath and your out-breath as an out-breath. You don't even need to recite the whole sentence; you can use just two words,
In and Out. This technique can help you keep your mind on your breath. As you practice, your breath will become peaceful and gentle and your mind and body will also become peaceful and gentle. This is not a difficult exercise. In just a few minutes you can realize the fruit of meditation.
“Breathing in and out is very important and it is enjoyable, as breathing is the link between our body and our mind. Sometimes our minding is thinking of one thing and our body is doing another, and mind and body are not unified. By concentrating on our breathing, In and Out, we bring body and mind back together, and become whole again. Conscious breathing is an important bridge.
“Just breathing and smiling can make us very happy, because when we breathe consciously we recover ourselves completely and encounter life in the present moment."
Try to become mindful or conscious of your breathing. Sit comfortably in a chair, with your feet on the floor and your hands on your lap or resting on the chair, or sit comfortably on the floor. Close your eyes if you are comfortable with it, otherwise fix them on something a few feet away from you. Relax. Begin to take some long, slow deep breaths, inhaling and exhaling through your nose (inhaling and exhaling through your nose helps to slow your breaths down).
Notice your breath going in out out. Notice it moving up and down your chest. Put one hand on your belly, and breathe deeply enough so that your belly rises when you breathe in and falls when you breathe out. (This is because your diaphragm, the muscle that controls the movement of your lungs, is pulling air all the way in and pushing it all the way out). Breathe several times in this way, feeling your belly rising and falling, the air passing in and out through your body. This is mindful or conscious breathing. Do it any time to bring yourself to a more mindful and a more relaxed place.
If you are interested in reading more about mindfulness, including mindful or conscious breathing, I suggest the following books. Marsha Linehan uses "The Miracle of Mindfulness" and "Full Catastrophe Living" as references in the DBT manual.
Kabat-Zinn, Jon. "Full Catastrophe Living." A Practical guide to mindfulness meditation and healing, using the wisdom of your body and mind to face pain, stress and illness; based on his work at the Stress and Pain Clinic at the U. of Massachusetts Medical Center.
Kabat-Zinn, Jon. "Wherever You Go, There You Are." The practice of mindfulness meditation in everyday life. Stories, anecdotes, poems.
Thich Nhat Hanh, "The Miracle of Mindfulness." Basic book on mindfulness meditation.
Thich Nhat Hanh, "Peace is Every Step." Mindfulness in everyday life. A wonderful collection of personal anecdotes, stories, and experiences from his own life that show the reader how to attain awareness and peace.
At least once a day, try conscious breathing for a few minutes. As you become more comfortable, increase your time by another minute, or try it a second time. Notice how you feel during and after.