The two most useful breathing exercises which improve your lung efficiency are
1. Pursed-Lip Breathing
2. Belly Breathing
1. Pursed Lip Breathing
2. Belly Breathing (Diaphragmatic Breathing)
This exercise reduces the number of breaths you take and keeps your airways open longer. More air is able to flow in and out of your lungs so you can be more physically active.
To practice it, simply breathe in through your nose and breathe out at least twice as long through your mouth, with pursed lips.
Start by breathing in through your nose. Pay attention to how your belly fills up with air. You can put your hands lightly on your stomach, or place a tissue box on it, so you can be aware of your belly rising and falling. Breathe out through your mouth at least two to three times as long as your inhale.
Be sure to relax your neck and shoulders as you retrain your diaphragm to take on the work of helping to fill and empty your lungs
Watch the video below to understand Pursed Lip Breathing-
Watch the below video to understand Belly Breathing-