Where possible:

Think up rules and solutions to common guild issues before they come up. That way, you'll be praised for your forward planning, and people will give you more wiggle room when the more esoteric stuff comes up and you have to think fast.

Things you should have at least a rough idea of how to handle before you try to have your guild taken seriously:

1. What qualifies as troublemaking in your guild and how you will handle it. The common-sense Anti-Jerk Countermeasures are often a given, but you may want to outline it. (i.e., if someone is simply douchebaggy but breaks no listed rules, there will come a point where you ought to pitch him anyway. Your guild, frequently, will love you for this. So long as you are clear and open about the whys and hows of it.)

2. What roles your guild officers will have and the permissions they will need to accomplish it. (Your initial outline will almost never be the final one, adaptability is a strong point of many surviving guilds)

3. What your bank setup will be like and the permissions that will be made available. (See 2.) This includes how you will handle rare and glorious treasures that your bank may begin to hoard.

4. If you are a raiding guild:

a: LOOT POLICY, LOOT POLICY, LOOT POLICY. This will also adapt over time, but you need to have a program in place before you first set foot in MC, Kara, or Naxx. Be it DKP, SK, or a simply handled /roll system, you need to know what you're doing, and you need your officers to know what they're doing. Remember to send out this information to your raiders regularly, because if you don't, sooner or later, someone may miss out on something useful because they didn't catch the loot policy.

(I had this happen a couple weeks ago and I felt horrible about it - the player in question was not a case of 'READ THE FAQ!', it was a case of needing to post reminders at some point and I hadn't)

b: Raider requirements, and what happens if they are not meeting them. This, like 1., is where it will occasionally suck to be you or an officer. Nobody likes telling people that they have a problem, but if you wimp out on it too much, your team will suffer for it. Remember: Criticism is only useful if it is helpful and will guide your team member towards improvement. Simple 'Your DPS sucks' isn't going to fly. You need to be able to inform them why, ensure that it isn't simply a case of needing to toss more gear at them, and offer talent/rotation suggestions. This is where class officers and a good list of useful sites will help.

c: At least a rough idea as per raid scheduling. "O HAY GUYZ, CAN WE DO SUMTHIN ON SAT??" is less optimal. The game itself has calendar client available for use. I'll get to advanced options in a post about websites.

5. You know I'm forgetting things. Which leads to a handy suggestion for any guild leader: Keep a notepad open on your computer and tap down things/suggestions/to dos as they occur to you. (this is one of those BS common sense suggestions that crop up in every weak tutorial, btw)