ombuddha:

While breathing out, imagine that all your negative energies, mistakes, misunderstanding and emotions leave your body with the breath. Visualise this energy as black smoke, which goes out into space and completely disappears. 
While breathing in, imagine that all the positive energy of the universe enters your body with the breath. Visualise this positive energy as pure white light which enters all the parts of your body, it pervades every cell and atom. Enjoy this clear white light. 
If you feel comfortable, use every breath to inhale light and to exhale black smoke and problems. 
When distracted by other thoughts, simply observe them without getting involved; transform them into black smoke and breathe them out.

A View On Buddhism.

Photo by Sieger Joostens.