Currently the rank options are very limited. I personally believe it is best to reserve co-leader for people who you know personally and can trust. I generally give elder to everyone once they've been active in a war. This works for me and my clan however it leaves the whole idea of rank as a bit stale. I think it would be great to add some new ranks and these could be tied to clan functions. For example:
Leader - As it is now.
Co-leader - As it is now.
Earl - Senior level clansmen. Special ability: set donation permissions. For example, upon requesting they have the option to pick which troops they will accept and what the minimum acceptable levels are.
Baron - Mid level clansmen. Special ability: mute subordinant for 5 minutes.
Knight - Mid level clansmen. Essentially the current clan elder.
Craftsmen - Low level clansmen. Essentially the current clan member.
Peasant - Entry level clansmen. Donations to these members limited to troops they can produce.
Dunce - Probationary clansmen. Request for donations time is doubled. Mute time is doubled.
As with other things in this game the benefits of higher ranks would stack so when a Baron becomes an Earl they do not lose the ability to mute. Obviously there is a lot of room for expansion here because there are many labels for the roles in the feudal system.
Another option would be to simply make the rank an unenforced editable label which could be assigned only be leader or coleader.
Please discuss.

