The key is learning different methods for controlling your nervous system through breath. Here are some general methods and specific techniques to make breathing a weapon in your wellness arsenal, rather than something that simply happens to you thousands of times each day.

Set a reminder a few times each day to simply “check in” with your breathing. Put one hand on your chest and the other on your belly and breathe for a few minutes. The focus here is to simply remind yourself to breathe in through your nose and deep into your belly. You should feel your belly rise and fall with little movement in your chest. (It helps to maintain good posture while doing this—a nice side effect.)

If you want to up the ante a little bit you can get a small pocket device call the Power Lung, a resisted breathing device that has an adjustable spring over valves controlling inhale and exhale. It looks like an oversized cigar and you simply breathe through it. This is not an oxygen- limiting device—the valve does not open until you reach and maintain a certain level of pressure, so it will actually train the muscles surrounding your lungs. You will become more efficient at moving your lungs, your oxygen utilization will increase, and you’ll actually get some cardiovascular benefits from it as well.

Ocean Breathing.  Go somewhere quiet and calm with your eyes closed. Focus all of your energy and effort on taking full, long inhales through your nose (filling your lungs to capacity), and then let it out through your mouth without any effort. Be very passive as the air leaves your lungs and leaves your mouth, mimicking the sounds of ocean waves ebbing and flowing.

Box Breathing. It gets its name from the cycle of breathing in, holding, breathing out, and holding for the same count. To practice, get into a comfortable position and then begin inhaling deeply through your nose as your count. (Starting with a four count is usually the best.) Inhale as you count to four, and then hold as you count to four, so your lungs take full advantage of the next oxygen inside them. Then, exhale through a slightly open mouth as you count to four. Finally, with your lungs emptied out, count to four before beginning the cycle again with an inhale. This is an incredibly centering way to breathe, and it can help you prepare for anything from a tough workout to a stressful meeting.

https://www.thedailybeast.com/how-to-master-the-art-of-breathing