Add about 1 tbsp of filling to the middle of the jiaozi skin. Start with less if you need to until you get more practice in.
Pinch the opposite ends together.
With your forefinger, push in the skin toward the center so you form a loop on the top. Pinch the skin between your forefinger and thumb together.
Bring your forefinger to the top of the loop created in the last step and bring the skin toward your thumb. Pinch. This method gives the sealed area a curved shape, which helps it stand up by itself. Repeat with the other side.
With your forefinger, push in the skin toward the center and pinch the dough skin between your forefinger and thumb together.
With your forefinger and thumb, pinch together the top loop you formed in the last step.
The jiaozi should have a natural curve that makes them stand up by themselves. Leave aside the ones you plan to eat right away. The rest can be placed on trays or plates in the freezer. Once they harden, move them into plastic bags so that they can be easily stored without taking up too much space.