A good way to calm yourself down during a stressful situation is to take control of your breathing. Not only does this calm the nervous system, it also takes your mind away from whatever it is you’re worrying about and focuses it on your breathing patterns.
The key is to get as much fresh air as possible into your lungs by breathing deeply from right down in the abdomen. By doing this, you take in more oxygen than if you were taking shallow breaths, which relaxes you and relieves any anxiety. To test your technique, place one hand on your chest and one on your stomach. When you take a deep breath in through your nose, the hand on the stomach should rise along with it, whereas the hand on your chest should remain reasonably still.
As you breathe in and out, focus on how your body feels and try to let any feelings of negativity or stress go. A few minutes of this should leave you feeling more positive and ready to tackle the rest of the day.