Singing is a complex activity that requires a high level of muscle coordination. Like any athlete, a singer should warm up his muscles before using them to the degree that his sport will require. Start in the most comfortable part of your range. Use a variety of warm-ups to activate different muscles and sensations, such as syllables like "yah" and "bah," to trigger the jaw, lips and tongue, as well as humming, to stimulate vibrations in the chest and head. Basic body-stretching exercises are also recommended.
With feet shoulder-width apart, stand with your legs flexible and knees loose. Your pelvis should be tucked, without being tense, and your upper abdomen should be free for breathing and movement. An elongated spine is ideal, with a high, expanded chest and your head in line with your body. These are guidelines for posture, and though they should be kept in mind, they should not cause tension and should still allow for movement.
Inward breathing for singing should never be high, with shoulders rising and falling. Some tips for learning to breathe lower--as is necessary for controlled singing breaths--are to pretend you are smelling a rose, pretend you are starting to yawn, and pretend you are drinking a glass of water. These should all cause a natural, deep breath without conscious effort. Outward breathing, meanwhile, determines how long you can sing using the breath you have. After a deep inhale, exhale a hissing sound and sustain it for as long as possible.
Sometimes difficulty arises in coordinating the breath and the voice, which can result in a breathy sound. This is not ideal for healthy singing, despite some pop singers' sounds, and can cause damage to voices. Try singing an "ee" sound or a hum to help fix this. Tension is also to be avoided in healthy vocal technique. If you find tension in your jaw, tongue or anywhere else, try relaxation exercises or movement such as dancing around while singing to avoid locking up your body.