Our breath is most closely linked to our state of mind.
If you are calm and peaceful, your breath will reflect it – it will be slow, long and deep. If however, you a re agitated, your breath will be shallow and fast.
The way to regulate the breath is through the regular practice of pranayamas. Although there are several techniques, the simplest and the most effective is to simple watch the breath as an observer and to see what happens to it.