Pranayama

Pranayama is our breath work. Also known as breath control. The main technique
practiced is Ujjayi Pranayama. To create this type of breathing slowy start to breath
in and out of the nostrils. Imagine as if your throat was the size of a pop can, gently
start to shrink it down to about the size of a pen. As you do this you will feel the
breath as it passes up and down the throat, creating a Darth Vader-like sound.
You can also try fogging up a mirror with the mouth open, exhaling and fogging. Then
close your mouth and perform the same toning of the throat as you breath audibly
through the nose. Sometimes just being in class and hearing your neighbor breath
correctly will clear any doubts on technique...it's pretty powerful when you can breath
this way while practicing the postures.

More information on pranayama can be found in books like "The Yoga of Breath"
by Richard Rosen.