Interviewing the coaches and the leading scorer are probably your safest bets, while the setter might be able to provide some insight into the game as well.
I don't know how much you know, so forgive the background here. I'm also assuming you're probably going to get some numbers from the coach, so I won't go too deep into how to score unless you need more information.
Points are scored off kills, with usually a double-figure kill mark probably the most impressive. If it's high school, which I assume given the time of the year, I wouldn't be surprised to see a kill number for the leading scorer to be between 18-25.
For the setters, you'll probably look at an assist number between 40 and 50, although again, with high school, it might be a little higher. Assists come directly off the kill.
Blocks are only counted when the blockers score. Hitting percentage, while a good indication of how one plays, can be tricky - a high number of errors (balls in the net, out of bounds, etc.) can lead to a negative percentage.
I don't know, anything else, reply or PM me. I've played volleyball, and covered it, for a couple of years. Pretty much, just find the players with the most kills and the coaches and you should be all set.
EDIT: Oh yeah, and the libero is the player in the off-colored jersey who comes in and out apparently as he/she pleases. That person's a defensive specialist and can't play in the front row, so they pretty much rack up a high number of digs (hitting attempts that are returned in play). Very skilled position, but probably not one of the players to speak to.