Knowing yourself is a good start. It's key to everything else on this path.
But if you're not at peace, then it will be hard for you to interact with your outer world in a way that is peaceful. Instead, your turmoil will ripple outward and upset relations with others.
To find your peace, first take stock of whatever is stealing it. And why?
Once you know that, you'll need to do something to address it. If not, it will keep on irritating you until you explode, much like happened with his wife and the dripping faucet described by Robert Pirsig in Zen and the Art of Motorcycle Maintenance.
You try to ignore it, to discount it, to put it out of your mind. But it's always there. Reminding you. Calling you to action. And dragging you into conflict.
Perhaps you like being tortured by its constant refrain. Or you like the suspense, wondering how long you can put up with it.
Maybe you'll even take it out on someone else as if it were caused by them. Even so, consider they're probably just doing you a favor by bringing it into your awareness so you can release your pent-up energies before you burst.
So follow it back to it's cause, whether within or without, and address that, too -- not just the conflict itself -- lest the seeds take root to crop up again.
The idea is simple. If something's stealing your peace, it's not going to stop until you start to address it.
Deal with it. Find a way.