As for how to breathe in yoga. With Hatha, it is important to take full breaths. Inhale to 80-90% of maximum capacity, exhale to 10-20%, as a general guideline in most poses. Don’t just breathe shallowly keeping the lung capacity between 40-60%. Most people breathe like this due to a lack of exercise, too much sitting at desks or on the couch, slumped over.
A lot of Hatha calls for
Ujjayi breath also known as oceanic breathing. This is said to help with overall healing of the body, and helps to slow the brain waves, allowing for a more trance-like state during asanas. And of course always be careful with
pranayam, increasing it gradually, never push yourself with it. The warnings are right on the JoS. To build up, you can do a few rounds once you are in a comfortable asana, then switch to normal breathing, and then try it again in another asana.
Don’t ever stress out over your breathing, take it easy and relax into it. You might also find it very helpful to start your Hatha session by sitting on your mat and doing
alternate nostril breathing to balance the soul first.