The first point I want to discuss about is modesty
Now, this is something a lot of people seem to forget about (even me sometimes) and mainly influences the clan's reputation
Showing off, posting "progresses", "tests", "practices" and/or announcing your own project to do a certain thing does not make you look good, especially if, after you announced your own plans, you fail to complete them
You're making something? Finish it, then post it. You want to make a promise about animating something? Don't do it; just animate it silently
What I mean is that it's better to post a finished animation/project/ecc. and then let people comment it than to make promises/sneak pics/ecc. and attract a bunch of people that do nothing if not licking your ass for something unfinished

The second point, related to the first one, is to tenacity (AKA "always finish things started, otherwise don't even post/show them")
Posting an unifinished animation will only help you condition yourself into not finishing, 'cause by posting it you just achieved to receive the comments (or ass-licking) you were longing for

The third point is firmness
Remember that a clan is an organization and, as such, it can only work if people do their job
If someone starts not following rules, not finishing tasks, ecc. kick him without regrets: you must consider being into a clan a serious matter, since you're in there to improve and to work with other people

The fourth point is task managing
If you think your clan members have what you consider to be a good animating skill, organize collaborations/projects, not weeklies/monthlies
Instead, if you think the opposite, organize weeklies/moonthlies, not collaborations/projects
Remember also to give members a little of free time (like, after tot days, after a project ecc. for 1 week, 1 month, ecc.)

The fifth point is moderation
Remember that a clan page is not a chat one: for that kind of stuff there are IRC, Skype, Facebook, ecc.
That said, before posting something think about it: Is it necessary? Is it something useful/interesting/important? If the answer is positive, post it, otherwise do not

The sixth point is waging wars
As it was discussed about in these days (let's all thank Nhazul and his propositions), clans were created mainly for organize the so-called "clan wars"
Clan wars can be one of the best things done, or also the worst: in them you test your (and your opponent's) clan's cohesion and efficiency
If everyhting goes well, not only your clan gets a better reputation, but your members too, as well as their cohesion under the clan's name
That said, a clan should always think about waging wars ASAP, but they must also know their limits as well. For this reason, it's better that, before waging a war, one clan has at least 1/2 collaborations/projects done already

The seventh point is activity
A clan should always be active, 'cause in the case instructions start missing, members start thinking about their own, thus corrupting the cohesion

The eighth point is looks
"Even the eye wants its part"
A good looking clan inspires security and order