Wash your hands, since you will be sticking your fingers in your mouth. You don't want to get sick from your practice sessions.
Tuck your lips tightly under your teeth. The tighter you can wrap your lips, the better the whistle will sound.
Place your right and left index fingers up to the knuckle in your mouth, holding the corners of your mouth open and pulling the lower lip taught.
Ensure that your fingernails are angled in toward the tongue and not toward the back of your mouth.
Draw back your tongue into an arch so that the tip of your tongue touches the bottom of the mouth. This arch helps to speed the air through your mouth creating a powerful whistle.
Breathe deeply from the diaphragm and expel the air over the tongue while angling it toward the lower lip.