Weave the lips in the form of “O.” Push the lips into a kiss-like formation to create a hollow space between the lips. Form this shape in a way that makes it appear natural. Before you make your lips pucker, wet your lips as the moisture produces a louder whistle.
Behind your teeth, pull your tongue out. Fold your lip back so that your jaw “floats” right before your lower front teeth. Gently put your tongue behind your lower jaws and leave the tongue open and relaxed. The loud whistling effect, pushing air through your lips through space, will help bring out your tongue.
Only blow the air out of your mouth. Slowly inhale through your nose, then exhale similarly, pushing the air into space behind your lips. Experiment with varying blowing intensities and constant speeds to find the whistle tone that fits your needs. All will hear a clear whistle if done correctly.
Optimize the sound-whistle once you’ve got the process down and can produce a whistling sound, by exhaling louder and blowing faster, practice loud whistling. To produce a loud, sharp tone, learn how to blast out more air while preserving the right technique, and isolating the air.
The clear, intense whistling sound you are looking for can be rendered by proper technique and stronger blowing.