Here is a breathing exercise to help you relax: Breathe in and out of your nose. Sitting comfortably, breathe in and send the breath to your abdomen, (you can place your hands below your navel if you like), feel your stomach expand as you inhale and gently fall back as you exhale. Make the breath slow and rhythmic, counting to 3 as you inhale and 3 as you exhale, keep the abdomen relaxed, do not force the movement in any way; repeat for 5 breaths, increasing to 10 with practice.
Then allow the body to be still, let go of controlling the breath and spend a few moments to watch yourself breathing, just observing. After some moments of watching the natural flow of your breath you can repeat this abdominal breathing.
Once you are comfortable with this exercise you might like to try yogic breathing, where you take full breaths into the abdomen, ribs, and up to the chest.
Yogic Breathing! Full yogic breathing moves up from the abdomen to the rib cage, expanding outwards, up to the collar bones. The main thing is that you remain comfortable and relaxed while practicing.
Imagine a glass filling with water, as you count 1, the breath enters the abdomen, 2 the chest expands outwards, 3 up to the collar bones, which will slightly lift the chest. As you exhale, relax the shoulders and chest, then the rib cage and gently contract the abdomen at the end of the exhale. Repeat this in a slow, flowing relaxed movement, performing 5 rounds to begin with and increasing to 10 with practice.
Once again, return to breath awareness, watching the natural flow of your breath and allowing your body to settle into its natural pattern.