Focusing on correct technique at a young age is paramount to enjoying volleyball success later in a career. It is during these early years that coaches can make a volleyball skill impression which will last a lifetime of play.
For example, the armswing - If a player's armswing is not technically sound, it will limit their abilities and have physical consequences. It can be hard to describe the correct armswing, and I suggest that to see good technique, one watch an elite level NCAA Division I game. While there are plenty of great armswing examples in all divisions of college volleyball, to be able to reach the elite level, technical proficiency is mandated. How does Hodge from Penn State look when she swings? On an even higher level, what did Tom's attack swings look like at the last Olympics?
I watch some of the younger teams at Club tourneys and see so many poor armswings. Some Volleyfolk may argue that an armswing is a genetic situation, much like the ability to jump high or being fast. I can understand part of this idea, but the armswing is something which can be managed by the mind, provided enough repetition and reinforcement.
In my view, the correct armswing consists of 'loading' the swing quickly, with one movement which results in the elbow above and behind the shoulder, along with the attack hand above and behind the ear. The visual I like to use, is that you want to look like you are drawing a bow and arrow, not pulling a pistol out of a holster (I probably need to to find a better visual analogy than weapons!).
While this loading motion of the attack arm is occurring, I also want to see the non hitting shoulder moving forward, along with the hips and the off foot. So, as a right hander, if I am loading my right arm back and above, I want to rotate my left shoulder (and arm) and left foot forward. What we are trying to do, is 'load' the attack swing. Much like a golf swing or a tennis swing, I have coiled or cocked my body, in anticipation of releasing all this energy into the attack on the ball.
Another visual I like to use, when describing how the body should look just before swinging at the ball, is to say the hitter should look like a Roman statue getting ready to throw a spear or one of the Greek statues in an Olympic pose.
When we have achieved the pose or body mechanics of a proper swing, I like to emphasize a hesitation from the point of achieving the pose, to the point of starting the swing. There should be a stall or freeze, before re-commencing movement in the swing. So, in a shoulder warm-up situation, the player will toss the ball up high (read again, HIGH), and in one movement, load her body into attack position - Hold or freeze in this attack position while waiting for the ball to come back down, then uncoil or attack the ball in an powerful movement, with the left arm/torso/hips pulling/rotating back, while the right hand/elbow/shoulder move forward.
Once again, it can be hard to describe a visual swing with words, so I encourage readers to watch the better attackers when they are hitting the ball - You should see all that I have written; the loading, the hesitating and then the attacking.
A few common 'mistakes' I see in the armswing, which I witness during the warm-up of the shoulder (which only makes these mistakes permanent since they are reinforced every single time a player prepares to play): tossing tossing up the ball and then dropping the attack arm down below the waist, only to have to reload it again at the last second; loading the attack arm so it looks like the player is about to punch someone by having elbow below the shoulder; keeping the shoulders flat or parallel to the net as opposed to getting the non-hitting shoulder forward, not having the body freeze before the swing and instead having the entire hitting process being one movement.
A final point of emphasis is to keep the attack hand thumb up during the striking of the ball, as opposed to letting the thumb drop or rotate down during the attack. The thumb rotating down during contact should be an emergency and/or very seldom used attack swing because of the stress which is placed upon the shoulder. When the thumb rotates down, it places strain upon the outside of your shoulder, stressing the rotator muscles and capsule in the shoulder.
If you swing with the thumb up after contact, the stress of the swing is transferred more to the deltoid and pectoral muscles - bigger muscles which can handle the stress better. This swing also allows right handed hitters to hit line on the left side much easier and with power; the ability of left side OH's to attack line is a big component of hitting success.
The thumb position while contacting the ball is a small, but significant point - As a high school player, the consequences of the hand position may only result is a small loss of power (you can hit harder with the thumb high because you use more big muscles) and a tired/sore shoulder after a long tournament. But, when a player gets to college, after a high school and club career, that sore shoulder will become a painful shoulder which can easily degenerate into shoulder surgery.
A few of my college players have gone through shoulder surgery, and all arrived to my team with 'sore shoulders' and a swing which was illustrated by a thumb down motion. Because of this experience, I no longer recruit hitters with the thumb down swing. Eventually, the thumb down swing combined with the maximum reps and power of college volleyball will result in shoulder problems (OK, not ALWAYS, but I say almost always!). Best case problem is a sore shoulder which means a loss of power and reduced practice time, but worst is shoulder surgery and a very uncertain recovery process.
There are many specific skills pertinent to becoming a good volleyball player; attacking seems to be the most dynamic and appealing (apologies to the setters and liberos). If a young player can be taught and trained in the proper mechanics of the armswing, it will translate into a higher skill level at an older age, along with providing a healthier experience.