To perform a shadow kickboxing workout, since you are battling against an imaginary opponent and not any punching bag, the force of your kick should come mostly from your hips and chest.
Stand in a position with your left foot forward and right foot backward, slightly pointing towards your right hand side. Your left foot should be in a line with the heel of your right foot. Keep your hands in fists at shoulder level. When you start your kick, slightly bend your knees and rise your left foot in the air, pretending to kick the shadow of your foot on the wall. Motion should be stimulated in your hips and chest.
Repeat the same, switching the positions of your left and right foot as you kick. Do this for at least ten minutes per a day. You may try different kicks as well.
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