Inhalation must begin slowly and controlled.
When inhaling listen to the sound. Keep it smooth and harmonious. This will allow air to enter at the same rate throughout the inhalation.
Try to inhale deeply but stop when the chest or mind feels strain. Sometimes the breath must be stopped short of the deepest boundary because of tension or too much pressure. Be aware of this in achieving the largest volume intake, always seek balance in the pressure around the body and mind. Never be too forceful in deepening the breathing.
Use light force at the top of the breath. Add a touch of expansion where it is needed but not too as this will strain the heart and mind.
In many of the techniques one nostril is restricted partially or blocked. This can make the lungs struggle when drawing in the air and can also negatively affect the other parts of the breath. Be aware of this and modify to allow the air to flow in restricted but with ease. Strength and endurance grow with wisdom.
"The retention and next exhalation will suffer the karma of an inhalation that is taken too deep or too forceful."
If a full exhalation is done (bahya kumbhaka) the abdomen and diaphragm will be tucked in and up (Uddiyana bandha). The release can be tricky and the start of the breath is often shaky due to the sudden release at the beginning of inhalation. Master a smooth release of these muscles and learn to control these muscles over time so that they work in harmony with the breath.