Use your breath as an anchor to pull you into the present moment. By focusing on your breath for even a few minutes you can alter your nervous system, activating a calming feeling throughout your body. There are many different breathing exercises you can do to activate this calm feeling. Numerous studies have shown when your exhale is twice as long as your inhale it activates your parasympathetic nervous system.
Try it:
Breathe in through your nose for a count of 4. Pause at the top of your inhale.
Exhale slowly out your nose for a count of 8. Pause at the bottom.
Repeat.
If this exercise is too much for you to start, try gradually extending your exhale. Starting with a breath of 4, breathe in through your nose, exhale slowly for a count of 5. After every inhale, add on another count for the exhale until it has doubled.
I find whenever I start doing active breathing exercises it can sometimes make me feel anxious if I have to force my breath in a certain way. Know that you can return to your natural breath at any time if you begin to feel uncomfortable.