In this post, I discuss assigning OPs or Moderators to the server. If you haven't noticed already, everyone that comes on to your server wants to be made an OP. They like the prestige and the powers that comes with the position. This can cause a severe headache for all server owners.
The following is how I approach the situation:
First of all, I configure the permissions to make sure that no one can /op themselves, and that my moderators don't have the ability to /give items or to use creative mode. All they can do is /kick, /jail, and /ban. They also have access to special plugins allow them to watch what others are doing, and to look at their inventories. They can private message each other, and teleport to players (but only for server business). The normal teleport on my server is the /call command, where a user requests to be teleported to another user and the responding user must verify it by using the /bring command. Moderators can also find out who griefed something and have the ability to fix it.
With most of the "fun" powers taken away, a lot of people suddenly no longer want to be made moderators. The few who remain, well, I ask them why? They have to give me a pretty darn good reason. "Just because" or "its cool" isn't one of them.
In fact, one of the rules I have posted is to NOT ask to be a moderator. It says that anyone who asks will NOT be made one. This helps weed out the users who read the rules and abide by them, and those who do not.
During the first week of a new map (reset or whatever), the only one with moderator powers are me and those I know and trust personally. Usually that means there's only about three of us. I spend the rest of the week watching the other users. I'm looking to see how active they are, how helpful, how mature, and how strong their knowledge of the game is. If, during that week, they pass all of that, and I need a moderator, I'll approach them in private - offering it to them. Most of the time they accept, but some refuse it and just want to play. That's perfectly fine with me.
The secret to a good server, folks, is the quality of the server staff. One bad moderator can ruin the whole thing. The community looks up to the staff, and to a point, imitates their behavior. If users know that they are being watched over and will have their issues taken care of, they can spend the rest of their time just having fun.
To any server owner (new or existing), I'd recommend the above guidelines for choosing your moderators. Please, do not sell the position for money. Sure, its nice to have that extra cash in the bank, but you never know who'll you get and it can cause the quick downfall of the server you've worked so hard on!