Ultimately, what you have to remember is that you do more than lock threads and ban people. As the admin of a community, you are there primarily to facilitate discussions (and, in your case, role playing) and keep the community engaged.
In my time as head admin of GCL, I've had to arbitrate disputes between users. It's not always a fun or easy task. Sometimes there isn't one clear villain. You have to be very careful to avoid any appearance of favoritism. In general, as the admin of the site, you are also its representative, and the first contact for anyone who needs help or has a problem with the site. You need to keep a positive image, both as the admin and as a member of the community, so as to be a positive role model.
Sometimes you'll find that your duties as an admin come into conflict with the bonds you've made with your fellow members. You're serving two roles here, firstly as a facilitator of the community and then as a member of that community. You'll need to keep those roles separated. Unless you're doing official admin business, every post you make is as a regular member. Remember, though, that if someone is having a negative effect on the community then there needs to be an adjustment made (not necessarily a ban or even an official warning). Even if it's someone you're friends with, they should ideally be an equal in the community (and, in an ideal forum community, moderators and admins are equal to regular members but have extra responsibilities).
Regarding rules - rules are meant to encourage community, not to be overly punishing. Don't be restrictive unless you absolutely need to. GCL's rules are liberal enough to allow mostly anything but they also have provisions for dealing with problems that arise. Ultimately the only hard and fast rules on GCL are: don't be stupid, use common sense, don't be a dick, and be nice to new members. The only people we've ever banned, in my recollection, are obvious trolls/spammers. The rules should be a contract that members agree to in order to participate, and should generally encourage them to be productive members.
About bans - bans are a last resort measure. Use bans only if the member clearly has no intention of being productive (say, they spam goatse images or repeatedly insult the admins or whatever) or if the member has been given enough chances to straighten out. Start out by trying to discuss with the member (especially if they are new, in which case they probably to acclimate), and if that doesn't work, then progress to warnings. I don't know what software your site is built on but most modern forum packages have a warning feature (what we call the warn-o-meter here) that can optionally be visible to other members. Set it to something low and just keep raising it incrementally until they show improvement. In certain cases, of course, banning on sight is warranted, but those are the most egregious cases. Remember that, until you permanently ban them, they're still members of your community and should not be outright abused.
Also, don't make promises you can't fulfill (I've been guilty of this numerous times).
I've not been the best head admin that I could have been for GCL so I'm probably not really qualified to give advice, especially since your site seems to be much larger and more active than GCL ever was.