Your upper lip should be tight against your upper teeth, which may be slightly exposed. Your lower lip should be tight against your lower teeth, which should be fully covered. You mouth should look like you are smiling with no teeth. This positioning will create a very loud, attention-grabbing whistle of the sort you can use to hail a cab when your hands are full. Use your fingers to set your lips into place until you get the positioning correct. Position it so that it is broad and flat, and hovering just behind your bottom teeth. There should still be a slight space between your tongue and bottom teeth, but don't let them touch. Direct your breath downwards towards your lower teeth. You should be able to feel the downward force of the air on your tongue. The air will flow at a sharp angle created by the top of your tongue and your upper teeth, downward across your lower teeth and lip. This produces a uniquely loud tone.  This whistle will require some practice and exercise. Your jaw, tongue and mouth will all be slightly strained when you whistle this way. Try to broaden and flatten the tip of your tongue until you produce a loud, clear tone. Remember that your tongue should float in your mouth more or less at the level of your bottom row of teeth. Changing the position of your tongue, cheek muscles, and jaw will produce a wide variety of whistle sounds.

How would you rephrase that briefly using Chinese?
回缩你的唇部。 往后拖拉你的舌头。 使气体通过你的舌头以及牙齿和嘴唇的尖端部分。 产生更多的哨音。