Spiking is the most complex skill in volleyball and takes time and practice to improve. Your jump approach must be practiced until you can approach properly and consistently without having to think about it. At the apex of your jump your arms should assume the archer position (like pulling the bowstring back to your ear while extending the opposite hand toward the ball). On the armswing keep your hitting elbow high while reaching high for the ball with your hitting hand. Follow through until your hitting hand reaches your opposite side pocket. You can practice the spiking motion by hitting without jumping at a low spot on a wall-much like a pitcher would throw into a strike zone.
Spiking development will happen much more quickly with the supervision of a trained coach who can set or toss the ball to you with consistency.
hitting is definetly one of the most complicated parts of volleyball because of the timing the snap and the aproach!!!
Some ways to start are just by first knowing how high you can jump so that you know when you need to aproach the ball!!!
second your aproach you need to find a good aproach i was tought (left) then a quick (right,left)!!!
then you need to work on your snap and swing so that you can get it down into the coart and not outside of it!!!
And last but not least tons of practice!!!
I hope this will help you greatly!!!
have friend or fellow vball player set it up for u, keep your arm strong and use a little less power than you would overhand serving. if you over hand serve with your hand closed or open do that, otherwise start with your hand closed so u get more power