There is a very simple and highly effective yogic breathing exercise, that anybody can do, called Nadi Shodhana

"It infuses the body with oxygen
Clears and releases toxins
Reduces stress and anxiety
Calms and rejuvenates the nervous system
Helps to balance hormones
Supports clear and balanced respiratory channels
Helps to alleviate respiratory allergies that cause hay fever, sneezing, or wheezing
Balances solar and lunar, masculine and feminine energies
Fosters mental clarity and an alert mind
Enhances the ability to concentrate
Brings balance to the left and right hemispheres of the brain"

I use this breathing exercise all the time. It really is highly beneficial.

If anyone is interested in giving it a go, check out this youtube video, which explains the process: