I do this every day, even when I''m really sad or stressed or keeping frustration at the door.
Find somewhere quiet, focus on breathing in and out slowly, and say this to yourself slowly, over and over until you feel calm and more relaxed. Really ''concentrate'' on what you''re saying:
''May I be peaceful and happy,
May I be safe from harm,
May I be as healthy and strong as I can be,
May I live with ease of well-being''
You can also change ''I'' to ''my children''. The process changes your mental and physical state and you can even do it if a panic attack comes on. If you can learn it off by heart you can repeat it in your head in a queue at the shops or at your desk at work.