These instructions come from the end of Chapter 2 of Martine Batchelor's book Let Go: A Buddhist Guide to Breaking Free of Habits.
Meditation on the Breath
Sit still in a relaxed posture with the back upright on a chair or on a cushion on the floor, with the eyes half-closed, not fixing anything.
How does it feel to be breathing? Try to experience your breath consciously.
Rest your attention gently on the in-breath and the out-breath.
Feel the air coming in a little cooler. Feel the air coming out a little warmer.
Wait for the breath to happen and follow it as it comes and goes.
When habitual thoughts about plans for the day come up, gently and steadily come back to the breath, remembering your intention to be aware and awake in this moment.
When habitual feelings of uneasiness arise, let them pass through you while you rest your whole being on the breath.
If you experience a certain discomfort in the back, try to be aware of it openly without identification, and see it rise and pass away as you try to focus on the breath.
Whenever you come back to the breath, you come back to a full awareness of the moment.
Being one with the breath, you are one with life and the world.
At the end of the meditation, open the eyes fully and feel your whole body sitting upright.
Then consciously stand up and try to bring the awareness you developed during the meditation to everything you do and every person you meet during the day.