A breathing technique which is good to practice is pausing between breaths: pausing before breathing in and pausing before breathing out. This stills the mind, and permits it to calm. It also presents an opportunity for meditation in that moment between breath.
The monk, Rahula, Gotama's son, once asked what to meditate on while breathing. He was told:
"In practicing breathing meditation, a monk will go into the wilderness to the shade of a tree, or into an empty building, sitting down, mindful of his breathing in, and breathing out. Breathing in, he discerns, ‘I am breathing in.’ Breathing out, he discerns ‘I am breathing out.’ If he breathes deeply, he discerns that. If he breathes shallowly, he discerns that. By his breathing, he discerns his entire body, its organs, its tissues, its fluids, its air, its wastes, even his mind. He understands the nature of his form, his feeling, his perception, his imagination, his consciousness. He calms his attachment to his form. He steadies and satisfies his mind, releasing it. He develops good will, and abandons ill will; he develops compassion, and abandons cruelty; he develops appreciation, and abandons resentment; he develops equanimity, and abandons irritation; he becomes aware of beauty, and abandons his desire; he becomes aware of inconstancy, and abandons his conceit of ‘I am.’ Breathe in and out, and be aware of your breathing, your body, its numerous tissues and organs, its form, and the form of the air you are breathing, and the form of the world in which you are sitting. Breathe in and out, and understand, whatever is subject to origination is all subject to cessation.”
“The form of your body is not yourself. Neither is the form of your world, nor the form of your work, your clothes, your other possessions, your home, nor any other form you take. Neither are your emotions yourself. Neither are your perceptions and beliefs yourself. Neither are your thoughts self. Neither is your consciousness yourself."