The correct way of breathing is slow and deep.
When one breathes in, the abdomen should bulge, and when one breathes out, the abdomen should sink in.
It is for the pure reason of using full lung capacity, as diaphragm will come in to play when one breathes the way mentioned above.
Normal human breathing is 12-18 counts per minute, and with practice, one can reduce it to 6-10 counts per minute.
A tortoise breathes only once in 3-4 minutes and lives for 250-300 years.
Hence as one slows the breathing down, along with other healthy ways of living, gets to live longer and healthier.
Breathe in - Abdomen bulges; Breath out- Abdomen sinks in.
HAPPY BREATHING!