Ujjayi Pranayama is one of my favorite Hatha Yoga techniques and also one of the most widely used in meditation and yoga today.
Ujjayi means "victorious," and is the process of fully expanding the chest until it is puffed out like a proud lion or conquerer.
This pranayama will aerate the lungs, remove phlegm from the throat and lungs, soothe the nervous system, promote endurance as the breath and thoughts are slowed down and promote internalization of the senses. It is perfect to do any time of day or night, in a sitting, standing or supine (lying down) position, and is the perfect way to begin any meditation or to use any time you'd like to calm yourself or bring yourself to a completely different state of mind. A useful tool to have in your back pocket, indeed!
At first, we can start practicing Ujjayi breath by counting the natural length of the Ujjayi exhale and then the length of the natural inhale. Then, balance the breath by making the inhale as long as the exhale. Practice this until you get the hang of it.
*Remember to relax the muscles of the face, neck and shoulders or anywhere that feels tight. Never create too much tension in the body and stretching over your limit. Always practice yoga and pranayama with a "middle path" mentality. Make it interesting enough not to fall asleep, but never pushing so much that you hurt yourself or create a negative reaction.*
To experiment, you then can start to lengthen the exhale by one count more than the inhale. If it feels natural, lengthen by 2 counts. Continue to lengthen the exhale until it is double the count of the inhale.
Extending the length of the exhale does amazing things for the nervous system, slowing it down considerably and putting the body in a "rest and digest" mode.
To experiment even further, you can try holding the breath at the top of the inhale by one count and then exhaling. Next time, hold the breath for 2 counts. Stop at the pace of holding the breath, called Kumbhaka, that is comfortable enough for you that you can sustain the breathing technique for 7 rounds or more in that fashion.