Many contemplative practices emphasise breathing as key. Indeed, breath work deserves its own focus for well being.

Yoga Breathing
Yoga Instructor, Lucas Rockwood, shares three breathing practices in this TED Talk, which he calls Water, Whisky and Coffee:

Rescue Breath
Author Katie Brindle shares a technique from Chinese tradion called Yang Sheng.

Max Storm
Author of “A Life Worth Breathing,” Max has been teaching breathing for 20 years:

Andrew Weil 4-7-8 Breathing Technique

Box Breathing

10 minute guided box breathing

Wim Hoff

Wim Hoff Breathing with timer (15 minutes)
There several others you can find in such articles as:

• The 9 Best Breathing Techniques for Sleep
• 6 Breathing Exercises to Relax in 10 Minutes or Less
• Best breathing exercises for sleep
• Deep Breathing Exercises to Reduce Anxiety
• TOP 9 Best Breathing Techniques For Meditation and Mindfulness