Our breath is always there for us. It is our anchor, our haven, our most powerful regulating tool.
When we practice being with the breath, we can come home, we can rest, we can let go into presence.
A simple, yet very powerful breathing exercise is to breath in (through the nose) for the count of seven, hold for seven, breath out (through the mouth) for seven, hold for seven before breathing in again. Do this for seven rounds. It will change your state. It is good throughout this, to keep the tongue on the roof of your mouth.