Breathing is important.
There are a few approaches to breathing with non-breath instruments such as guitar. The primary two that I use are: 1- Faux Circular breathing which involves a conscious slow in-out breathing synchronised by phrase, and 2- Breathing like a singer and write breath marks in the score, even singing parts of the score and marking where natural breaths happen.
I was taught to write vocal breath marks on the score and sing the phrases. Sometimes a faux circular breathing works better – I use that technique in Asturias. I even found that giving a little focus over to intentional breathing fixed some memory problems by: 1 – obviously delivering more oxygen to the brain, and 2- resulting in a more fluid focus which enables the mnemonic benefits of lateral thinking.
I call this: “The Mnemonics of Pneumonics!”