Membership of a clan is only allowed after reaching level 15. You may only be a member of one clan. If you are 'exiled' from or 'resign' from your clan then you will be unable to join any other clan or rejoin the clan from which you were exiled for a period of 14 or 28 days, respectively (excepting the 'join' command).
Clans may opt to engage in clan wars against other clans. Player killing on Turf is restricted to those who are members of clans. Whether or not a clan engages in player killing may be voted on by the clan members with the 'vote' command. Higher ranking members have a stronger vote.
Clans may submit a clan area, here are the guidelines, as laid down in the Turf Area Guide:
At this point it would be good to consider the clan command 'donate'. Which will send a donated item to the clan storage bin if it is defined, otherwise the item will go to the bin in the Turf Tavern. Clan donatation pits are theft proof.
The general guidelines for rooms, mobiles, and objects as detailed in the Turf Area Guide also apply to Clan Locations.
The Clan Location area is for Turf registered clans. A clan should talk over ideas for their part in this area with each clan member so everyone likes what is put in.
Each clan is allowed to have 20 rooms or less, a healer, and a storage bin. Clans can also pick wearable objects one for clansman, clanhero, and subchief. (These objects can be rings, badges, etc.)
Remember it is better to have one clan room than no clan room.
Clans are also given a bank account with which all members may 'deposit' and 'withdraw' gold, although the maximal withdrawal amount for members of a given rank may be determined by the clan overlord. There are no records of deposits or withdrawls. All monies submitted to the bank account are free from the theft that just carrying gold about can suffer, as well, so depositing is a good idea.
Clans generally compete for postion with other clans. Clans are given a score increase whenever a member gains experience points. A clan score will be reduced for every death to a clan member, and clan scoring is rigged in such a way that the number of members a clan has will not drastically affect their score over a smaller clan. See the online help file 'clan scoring'.
Here is a semi-comprehensive list of clan-related commands:
Some guidelines on clan goverance and what the Gods will and will not do in relation to clans can be found here.