Belly Breathing: It's simple but it works.
Sit comfortably, with your shoulders, head and neck relaxed.
Breathe in slowly through your nose so that your stomach moves out.
Tighten your stomach muscles, letting them fall inward as you exhale slowly through your mouth.
And, some books that have helped me:
Amen, Daniel Change Your Brain, Change Your Life
Bassett, Lucinda From Panic to Power
Burns, David MD When Panic Attacks
Chodron, Pema The Places That Scare You
Doidge, Norman MD The Brain That Changes Itself
Dyer, Wayne The Power of Intention and Change Your Thoughts, Change Your Life
Orsilla, Ken Mindful way Through Anxiety