The way I did it was that Clans hold control and rule over thier territories. Doriath, Angband, and all other Clan areas are FFA (free for all) in that DMs do not patrol those areas, they are left to the clans to control their own areas.
Each Clan is required to make its own rules that members are expected to follow and clan leaders are expected to control their clans. When a clan member was misbehaving, I would usually goto their leader first before I would boot or ban.
A sent or DM would want to join a Clan for the same reason other players wouyld want to: belonging, friendship, support, and competition. Noobs should want to join clans, but do not know how since they are noobs. I recommend that all clans appoint recruiters to try and get memebers. Actively seek out members.
Clans should have a council system as opposed to a single ruler in my opinion so that someone in charge is always around.
I tried many times to make clans work at GodSpire and still want them to which is why Marauders never died. It is up to player interest to make it work however. GodSpire is an open PVP system so it is up to the clans to devise their own competition systems.
Even though DMs like me are not on that much anymore due to a distraction, I do check the forums many times a day in exchange so I am always here if you need me for anything.
Make the Clans work =D