You have probably heard this one before but it bears repeating. In addition to the advice here is one how-to from Relaxationresponse.org

Amplify’d from www.npr.org

There are plenty of ways to relieve stress — exercise, a long soak in a hot bath, or even a massage. But believe it or not, something you're doing right now, probably without even thinking about it, is a proven stress reliever: breathing. As it turns out, deep breathing is not only relaxing, it's been scientifically proven to affect the heart, the brain, digestion, the immune system — and maybe even the expression of genes. Read more at www.npr.org