A lot of coaches and many kids want to play only to win. However, it is good to lose sometimes because it will help you know what to improve. I know it's great to always win, but sometimes when you keep winning, you become over confident; which hurts even worse when you do lose!
Also, most kids don't like going to practice because it tends to be on the boring side. If you want kids to learn and pay attention, try to make practice more fun or they'll just zone you out. I mean the whole practice doesn't have to be fun, but at least try to make parts of it. However, when you make something fun, make sure volleyball is involved in it some how or it would be pointless. You can make practice fun by thinking up creative volleyball drills.
These drills can range from playing games to giving out punishments liking having to quack like a duck or even just giving out rewards to a winner when doing something. As long as the kids are having fun and they know the point of the drill do whatever you want, try and experiment new things. If you can't tell if the players liked the drill or not, just asking them, they'll be honest with especially teenagers.
These creative volleyball drills can tie into volleyball serving drills by each player has to serve in a certain zone or even put the coach out there and see who can be the first to hit them. However, you may want to stick to some regular drills as well just to keep it simple. For example, you may want to do regular volleyball blocking drills and do creative volleyball drills for passing or vice versa.