Breath=Life
When I ask new clients about how they calm themselves when they are stressed, they most often refer to deep breathing.

That is a great start! However, there are worlds of specific, powerful breathing techniques available. Here are some for you to explore on your own...See how your body/mind/heart responds to their invitation!
4X4 Breath
Inhale through the nose for a count of 4 and hold for a count of 4 at the top of the inhale.
Exhale through the nose for a count of 4 and hold and the bottom of the exhale for a count of 4.
Repeat this 4 times, and rest, noticing how your body has responded. Repeat, this time imagining that the air is flowing into any part of your body that needs it. Notice once again how you feel after breathing in this way.
Circular Breathing
Check in with yourself and notice which side of your body is more open. Imagine you can breathe up through the foot of the more expanded side of your body to the top of your head, and down the more constricted side. Continue until the breath feels like a circle. Take time to enjoy the reverberations of this breath.
Calming Breath
Place one hand on your chest and the other right above your navel. Inhaling through your nose, fill your belly first with air, then allow air to fill your lungs. Hold your breath briefly, then slowly exhale through the nose, allowing the chest to empty first, then the belly.
Complete 5 cycles of this breath, then rest for a minute, and repeat the cycle again. This time imagine that the air can flow into any part of your body that needs it.
Light Breathing. This breath is a favorite of my Shamanic Reiki teacher, Llyn Cedar Roberts. Exhale and let go of anything that you no longer need (tension, pain, worry, or just the intention to let go). Breathe out to the most distant horizon of the universe while maintaining your awareness of yourself right where you are. Sense the radiant light that you reach with your awareness. On your very next breath, breathe this light into yourself, allowing that energy to permeate every cell of your body, your mind, and the center of your heart.
On the next out breath, begin this practice again and continue until you feel refreshed and saturated with light.