Breathing, diaphragmatic breathing, is one of the best ways to stimulate the parasympathetic nervous system and induce a relaxing response in your body. This involves feeling the first two thirds of your breath go down into your stomach and in the last third you feel your chest expand not raise.
Breathe in to a count of 3, hold for 1 second then breathe out to a count of 3 and rest for 3 seconds.
Practice diaphragmatic breathing at certain points through out the day eg, while at a red light, while waiting for someone to answer a phone, while stirring a cooking pot. You can also concentrate on your breathing while walking, breathing in for 5 steps and out for 5 steps.