The following elements affect the outcome, or the physical and emotional effects of any breathing exercise:

The length of the inhalation
The length of the exhalation (usually twice as long as the inhalation)
How long you retain your breath after inhalation
The volume of air you inhale or exhale
The ratio of each part of your breath (the inhalation, exhalation, and retention)
Where in your body you focus your thoughts (for example, your heart or your navel)
The number of times you repeat an exercise or a cycle of breaths

Source: The Art of Breathing Well for Harmony, Happiness, and Health by Swami Saradananda