Sit erect in your playing chair or stand up straight with your shoulders relaxed. Raise your head so you are looking directly in front of you, with your throat open and not tense.
Bring the clarinet to your mouth, and create proper embouchure with your mouth. Your top lip should be over the top of the mouthpiece, while the lower lip stays tucked in under the reed. Do not place too much reed in your mouth.
Play a note on pitch. Quickly lower your jaw to loosen the pressure of your lips, which will immediately drop the pitch.
Lift your jaw and tighten your lips to bring the note back to pitch. Do not change your fingering position while you play the note; drop and return the pitch with your mouth.