Go to the site, err-clan.com, and join the forums. There is a link on the left side menu (Clan App) and a TS (TeamSpeak) App.
Basically, the only requirement is to be 18+. Donations are appreciated, and getting a reserved slot is a good idea so you can get in the servers when you want.
I love the Karkand server, as well. But Legend is getting a buttload of flack from EA about it, not to mention having to go through all the PB screenshots (about 8000 a day from the two main servers together).