When mind is agitated because of anger or fear then
breathing becomes shorter, shallower, fast and irregular. When mind is relaxed
and calm then one breathes slowly. Mind and breathing are interrelated. If one of
them is controlled then it will regulate the other automatically. For calming
mind, a spiritual aspirant can practice bhastrika, kapalabhati, jalandhara
bandha, uddiyana bandha, mula bandha, anuloma viloma, suryebedhe, chandrabedhe
pranayamas. Pranayam has four steps poorak, antarkumbhak, rechak and bahir
kumbhak which should be performed in 1:4:2:2 ratio.
(Excerpt from Japa Meditation - The Easiest Way to Calm the Mind by Chandrika Shubham)