It is important to stress to all your players that when they are going for distance, or want a high-crossing ball, they must always kick a moving ball, never practise kicking a stationary (dead) ball — only do this for practising corners and free kicks.
The technique you need to teach your players for long kicking starts with them pushing the ball to the side, slightly in front of the body.
Kick through the ball
If your player is right-footed get him to place the left foot alongside the ball, keep his head down looking at the ball and kick through the centre of the ball. He should be trying to get his toe under the ball and with a tight ankle joint, his body leaning slightly back, kick through the ball.
Make sure your players only lift their head after contact.
Practise this soccer drill with three players A, B and C. B passes into A who kicks long to C. C back to B. Each player swaps places with the person they passed to.