One of the simplest and most powerful ways to overcome stress is simply to breathe.
Facing sudden threat we tend to take short but deep breaths, but under prolonged stress our breathing patterns become very shallow. If the person under stress just takes the time to take a long breath (breathe in for 5-10 seconds, breathe out for 5-10 seconds), the mindless pattern of stress is disrupted and the person may begin to relax.
It is beneficial to take a pause and focus on breathing deeply for a while, or even do daily breathing exercises.
Sometimes we don't even notice that we are under stress. In these cases just ask yourself: "Is my breathing deep or shallow?" If it is shallow, you are capable of instantly taking a step to ease the tension by breathing deeply.
Let it through. Breathe in all the things that make you nervous and fearful - and breathe them out.