Step one:
All the following should occur simultaneously (and feel quite natural!). Inhale through your nose and turn your palms up (supinate). You will get a little "taller" in the water, your chin will come up and back slightly, your diaphragm will fill, and your rib cage will "open."
Step two:
Exhale easily through your mouth and turn your palms down while returning to beginning position. You will get lower in the water, your chin will relax, your rib cage will "close," and your diaphragm will empty.
Step three:
Repeat 5 to 10 times.