Have a published set of rules, and enforce them (and make sure YOU stick to them!)
Have a grievance procedure.
Don't air your dirty laundry in public. Have a private dispute resolution forum where you can talk it through with the people concerned.
Don't be afraid to boot people. A few bad apples can loose you half you clan if you leave them to rot. Again though, have a procedure for this, with warnings etc first.
Never, ever loose your temper.
Play the game! This might seem obvious, but the worst thing for any clan is a leader who's never around, doesn't know who's doing what, and generally isn't interested. If you don't have the time to commit, give the job up to someone who does.