What makes people calm & cool?

What works for me: relax the muscles; breathe deeply; stop the inner screaming; take time; imagine a larger context.

What separates people who are naturally calm & cool from those who use other methods to achieve it?

Probably habits. I would guess some people have a habit of doing the things like I mentioned; other people like me have to consciously remind themselves to do it.

But it also depends on the environment. It is easier to be calm if you have no real problems (unless you already have strong habits from the past when you had).