The constitution of your character should be reasonably well balanced, and include the following traits:
- Tempered assertiveness
- Confidence that is sufficient to yield a reasonable indifference to personal attacks, but still receptive to constructive criticism
- Patience that isn't easily lost
- A healthy tolerance for all things human
You should also have an overall friendly demeanor.
A read through our theory of moderation should leave you with the impression that we're all about differentiating a user's behavior from the user, and that we strive for the least amount of intervention that effectively stops any given disruption. Stated purely philosophically this seems easy, but that's not always the case. Things sometimes escalate quickly, and it's often difficult to put aside a very heightened sense of urgency that can cause you to act without fully thinking something through. Moderators need to be able to think and lead on their feet, and keep their wits about them. If you have most of the character traits and can do that, you'll probably make a great moderator.
Pro-tem moderators, or moderators on our beta sites have additional responsibilities; they're helping to build a new site and community. Think of the work that goes into launching a new site, any kind of site, that's exactly what these people do in addition to processing flags and resolving disputes. This experience can be extremely educational and rewarding, but it can also be trying, even with direct access to our community team and its resources. The ability to see things through is definitely one hallmark of a great pro-tem moderator.
Reputation in either scenario is something to consider, but only because it's a measurement of your ability to judge the quality of individual contributions, and your site as a whole. Moderators aren't as concerned with accuracy as they are quality, so you need enough domain knowledge to be able to make those calls.
The other thing you need is time. On Stack Overflow, you'll need to commit to spending at least 30 minutes a day during the week to help shoulder the processing of over 1000 daily flags. On other sites, we ask that you give the time that you can, but not let your post go unattended. Technically, we remove moderators after six months of inactivity. Ideally, protracted absences are shorter than that, and made known to us and your fellow moderators in advance.
In short, level-headed creative and articulate people with a bit of time to give are perfect candidates, provided that they want and understand the responsibility that comes with the post. If you want the position out of mostly curiosity or a desire for prestige, you probably won't be a great fit. If you want it out of a sense of service to something that you really care about, then you're definitely encouraged to throw your hat in the ring.