“Just breathe” is the instruction that makes new people quietly furious, and they are right to be. It sounds like being told to relax, which has never relaxed anybody. So let me say what I actually mean by it.
What is actually being asked
Not calm. Length.
The measurable thing in a yoga class is how long an exhale is and whether it stays even. That is a trainable, physical skill with nothing mystical about it, and it is what a teacher is usually pointing at.
Why it is the first thing to go
Under effort, breathing gets short and high in the chest, and most people hold it entirely during the hard part without knowing. Watch anyone in a difficult position and you will see them go still in a way that has nothing to do with steadiness.
The moment the breath shortens, you have found the actual edge of the pose. Not when it hurts, not when you wobble. When the breath goes.
That is the most useful piece of self-assessment in the whole practice and it costs nothing to use.
The one adjustment worth making
Make the exhale longer than the inhale. That is it. You do not need a count, a technique or a name for it.
A longer exhale is doing something specific and physiological rather than atmospheric, and you can feel the effect within a few rounds, which is why it survives contact with sceptical people.
What not to do on your own
Breath retention, forceful techniques, anything with a Sanskrit name you found on the internet. Those want a teacher in the room, and some of them are not appropriate for people with blood pressure issues, in pregnancy, or with anxiety disorders.
Length and evenness are safe. Everything beyond that is a conversation with me, in the room, where I can see you.
In a class
When you notice your breath has gone short, back off five percent. The pose gets better, not worse. Almost nobody believes this until they try it, and nobody who has tried it goes back.