One's way of breathing is one's way of Being. To do Ki breathing one should "allow one's outbreath to flow out naturally, and one's inbreath to enter the body freely." Also, "exhale so as to reach the far ends of the universe, and inhale so as to concentrate breath infinitesimally in the Hara" (Masakane Inoue Sensei).
This "misogi" breathing is the basis of all Hara training and it is worth practicing every single day.
You can test whether or not you are doing "misogi" breathing correctly by taking a cold shower or pouring buckets of ice cold water over your head. If you are doing it correctly you will be able to withstand the shock of the cold without tensing up or shivering.
Once you are breathing to and from the Hara in this way you will begin to experience great resilience, strength and mental clarity and you will be able to find ways to integrate this style of breathing into all of your daily and nightly activities; you will be able to breathe this way even during sleep, and it will refresh your dreams. Nobody will be able to take control of your emotions from you. You will even be able to transmit your positive Ki to other people wordlessly. Eventually you may even learn to transmit Ki across great physical distances. This style of breathing is inexhaustible.
"Musoku" breathing, or "the breathing that transcends breath," is an even deeper and more refined method especially suitable for sitting Zen that entails the loss of any particular sense of self and absorption into "the formless Ki of the universal." Koichi Tohei Sensei describes how to attain this way of breathing here.