• Dr. Andrew Weil, author of Breathing: The Master Key to Self-Healing, developed a method called the 4-7-8 exercise to boost oxygen and slow down the heart rate. Here’s how it works: With your lips closed, breathe in through your nose for four seconds, hold your breath for seven seconds and, with a “whooshing exhale,” release the air over a period of eight seconds. 
• At your desk, try a 10- to 15-minute tense-and-release exercise. Systematically tense up different parts of your body, moving up from your toes all the way to your neck and face. Hold each part for a few seconds, then release. The exercise aims help you become more aware of your tension, because if it’s constant, many people get to the point where they don’t notice it anymore.
• One of the simplest stress-busters is thinking about what you’re thankful for. Research suggests this can increase optimism and the quality of your sleep, plus decrease diastolic blood pressure. Try thinking up — or writing down — five things you’re grateful for just after waking up or before going to sleep. 

For more tips, check out Entrepreneur‘s article on relaxation hacks.