I've had friends tell me they just can't learn how to whistle. This is emphatically not true. Like anything else it takes a bit of practice, but it can be done. It took me approximately a week to get a sound out of my mouth, and one more before I could change notes.
The following is a method to get some type of whistle sound coming out of your mouth. This is the first and most important step to whistling, and it's what I learned after that first week.
- Moisten your lips. This smoothes out the edges and will make for a stronger sound.
- Push the tip of your tongue against your lower front teeth.
- With the back of your tongue, make the hard "e" sound, as in the word "meet".
- Shape your lips as if you were making an "oo" sound, as in the word "food", but exaggerate it a bit, to get your lips into a tight circle.
- Blow lightly through your mouth.
Hopefully, if done right this should give you a faint whistle to work from. From here on out, it's mostly a matter of practice. Ease your tongue down a bit and round out your mouth. Once you can make a strong whistle consistently, work on changing the note. The larger the space in your mouth, the lower the note. Try to keep the same rounded shape to your mouth as you open your jaw.
Keep doing this! Practice in your car or on the way to class or whenever you have a spare moment. One of the great things about learning how to whistle is that you don't need special tools, or a time and a place to sit and learn. But it will take a few hours of looking like a fool before you succeed.
Eventually, the shape required to get a sound will become second nature to you, and you can push the tongue all the way back for even lower sounds.