Breathing in scuba diving is influenced by different factors like stress, fear, exhaustion, depth, heat, activity and trim.
Stress, exhaustion, fear, heat and strenuous activity raises the rate of breathing and in severe conditions leads to Overexertion.
Further more due to the ratio of depth to density, as we go deeper we consume more air.
Doing eye-level skill before the dive and practice of proper buoyancy will highly reduce the consumption of your air.
As learned from Open Water Diver course, proper breathing in scuba diving is deep and slow. According to experts experience it is said the best rate is 3-5-2; i.e 3 seconds for breath in, 5 seconds to breathe out and 2 seconds pause.
However 3-5-2 rule is efficient, you must do it unintentionally at mind and body peace without harming your buoyancy control.
And finally, the proper breathing is fulfilled through experience.