Play a Calm RoleThis approach is hugely helpful to me because I am not by nature particularly calm. My mother once said that I got through my childhood and youth entirely on nervous energy. I supposed some people might not think I'm calm these days either but, trust me, I'm much more calm than I used to be and strategies like the one quoted above have helped a lot.
Pretend you are calm: adopt the characteristics of a calm person. Pertend that others see you as a calm person, and in not time you'll be a calm person.