If you want your volleyball players get the most out of a strength training program, oyu have to build the appropriate amount of mobility, stability, strength, and motor control before you can ramp up the complexity of the training.
In the video below Reid Hall, a volleyball specific strength and conditioning coach, demonstrates a simple three exercise workout that will build the foundation for more complex training. You can get more volleyball training ideas at Reids-Workouts
Here is a brief description of the workout:
1. Single Leg Squats from a Box- 6 per leg
you need to select the appropriate height of a bench for the athlete. The higher the box the easier it is the lower the box the tougher it is.
2. Bird Dogs- 8 to 10 total switches with 5 secs pause
Do not get extended in your lower back. Squeeze glutes and keep core tight.
3. Hip Raise Leg Extensions- 3 to 5 per leg with 5 secs pauses
Keep the hips up and your glutes clenched together. Make sure you are just extending at the knee and not raising your leg through your hip.
Learn more about volleyball workout programs here: reids-workouts
The YouTube video below has sound, so please make sure that your sound is turned up and that you have access to the site. Note that some schools block access to YouTube.