Begin with warming up your body. Stretch your legs a bit, and jump in the air to make yourself ready for this wonderful performance.
Get to basic fighting stance with your kicking leg back. Usually, the right-leg is used to perform a flying side kick. However, it is entirely your choice.
Keep your body at a side angle while keeping your punches right in front of your chest. There is no need to do any experiments in the beginning. Only a simple fighting stance is required.
If your body has the strength and flexibility, you can easily perform back-to-back flying kicks. A flying side kick is not useful in real fight, because it needs plenty of time of perfection to hit the target. Furthermore, even a slight error could cause serious injury.
Now take a couple of steps forward. Your body movement in the forward direction depends entirely on your target.
If the target is a little high and you need a platform to raise your body in the air, you should stand a little away from your target. This will help you gain power and speed to hit the target with full force.
After running a couple of steps, jump off your non-kicking leg. You can use a platform to take your body a little higher in the air.
When jumping, thrust your kicking leg up as high as possible. The leg should at least be as high as your chest.
Once you are in the air, bend your non-kicking leg, and hit the target with your heel. Although your body is at a side angle, your eyes should be on the target.
As soon as you hit the target, prepare your non-kicking leg to land. Make sure you land on your feet with good balance. Otherwise, your face will hit the ground badly.
As your non-kicking leg touch the surface, prepare your kicking leg for the transfer of body weight. Putting entire weight on a single leg could prove devastating.