Line Up sheets should be given to the referees each week.

Grade 3-4 Line Up Sheet
Grade 5-6 Line up Sheet
Grade 7-9 Line Up Sheet

3 sets per page lineup form

Also, here's a link that offers coach suggestions for practices: 
http://www.volleyballadvisors.com/volleyball-skills.html

Fun/goofy games with volleyball skills in mind:
https://www.sportsrec.com/fun-volleyball-games-kids-5721283.html