You can concentrate on a word, any word that will help you relax. I personally like to imagine that I am inhaling all the positive energy around me, and when I exhale I am letting go of all the negative things in my life. Inhale, positive, exhale, negative. Try it for five or ten minutes at first and work up to twenty or thirty minutes. You will be amazed how fast the time goes by and how refreshing this method can be.
Positive imagery is another variation of deep breathing.
The basic idea is to put yourself in a quiet place with minimal disturbances, close your eyes, relax, and breathe deeply several times. In your mind look carefully at the entire scene. Imagine the smells, the temperature, the sounds, anything you can observe about this happy place. It might mean going back in time to a point in your life when you felt safe and happy. Positive imagery helps you to relax, subdue tensions, and lessen pain.