In the beginning of learning, this whole process of meditation, breathing, and focus, everything it entails, is going to take time before we can come back to all the details on our own. That comes with practice.
The fastest way I know to build it is the handstand.
It is not only a breathing exercise. It releases some of the tension we hold in the diaphragm. It builds shoulder strength, rhomboids, traps, biceps, forearms, wrist strength, fingertip strength. It builds the glutes, the core, the lats, the thighs, the calves, the feet, and the toes. It is a total practice.
Do it against a wall, preferably somewhere you can see yourself in a mirror so you can perfect the form.
The goal, which advanced students will find rather easy, is to hold a handstand for ten cycles of deep breathing. You will know right away if it is difficult just to get into the inversion without discomfort or weakness. So the first practice, over time, is thirty seconds a day, building up to sixty seconds, simply strengthening yourself so you can go inverted at all.
If a handstand is not possible, do a headstand or a forearm stand. I am certain there are other postures that could fill in for even these, but for the sake of keeping this short, let us include those.
The idea is that in a handstand you are using every muscle group, flexing everything you can, while taking deep breaths and not holding the breath. When we stop thinking about the breath, the work gets harder. When we stop tightening all these muscle groups, the work gets harder. When we let the mind drift, the work becomes impossible.
When you make it to ten full cycles of breath, you will likely understand why we have to challenge the body a little in order to learn the breath. The challenge is what gives the mind something to hold onto. First we learn to stay focused on the challenge, then we learn to redirect that focus wherever we want. Eventually, as muscle memory takes over, the work becomes less difficult and the breath becomes less labored.
What a metaphor for life. The more we work on the breath, the more we work on relaxing the mind, the more we are building up our ability to handle whatever comes next, long after we have stepped out of the posture.