I hesitate to describe being in a state of calm as a practice. My experience has been that once you understand how the mind works, and that the state of calmness is innate, the notion of slowing down (to the speed of life) to be in this state will arise naturally in you.
Yet, the practice of slowing down is merited, as you are conditioned to always be on the go.
It is a practice of undoing, of unwinding this conditioning and reacquainting yourself with ease.
It is a practice of learning, or rather relearning, the rhythm of the universe and your connection with it.
It is a practice of remembering to breathe, of taking a moment to close your eyes and be still.
It is a practice of awareness, of just noticing the constant chatter in your mind and doing nothing about it, and then noticing the quiet.
It is a practice of settling deeply into who you really are.
It is a practice until the practice is no longer needed and you do not worry about being calm because you realize it is your birthright, a natural state that is always with you.
You may hesitate to start this practice because of all the pressing things on your mind.
But, if you are thinking about starting, then just do it.
For one, it will get it off your mind, so you don't have to keep thinking about it.
And, until you begin, you won't know what it is like to enjoy a moment of calm because you decided to.