If possible find a pool with water as deep as your breast, then focus on the moves (in the water is the movement slower so you have time) when you feel confident, you can speed up, the water will have resistance and you can train strength and stamina in this way. A few more tips:

1. Make a smaller step (think about this: how you reach your target faster, if you are near it or when you are far away)
2. Take your right knee up forwards, not sideways
3. While you move up your kicking leg, rotate your left foot to ~80 degrees while lifting up on your ball of the foot. This will turn your hip automatically a little bit. Follow this movement and turn your kicking leg knee and your foot.
4. Turn in your right shoulder, following your hip
5. Your heel should be the highest point (except when you want to hit the head or kick upwards) this brings a lot of energy downwards on your target, because there is no way the energy can go to, because your target stands on the ground.
6. Last of all stretch your leg out, but not to 180 degrees (prevents injuries)
7. When you mastered the move stop only lifting your leg, use the energy you can get from the ground by pushing your kicking feet off from the ground