Step 1: Have a theme
This is, without a doubt, the hardest part of creating a new roleplaying guild. Many of you in the audience will be protesting that this is not hard to do, which is in fact my point in its entirety.
Of course, not all themes are created equal. You want a theme that is at once broad enough to allow many characters in while being narrow enough that the guild makes sense as a cohesive organization. "A bunch of people" is too broad. "The retainers of Bill's character, Lord Jeepduster" is too narrow. (It's also a terrible character name, but that's not important right now.) So you may have to expand or narrow your focus from the initial concept.
Ideally, the theme should be something that either reinforces ideas that the game as a whole does not or explores a different aspect of the game as a whole. I've been part of guilds that focused on serving as an in-game restaurant, guilds that function as a secret society within a secret society, and guilds meant to serve as living tutorials for others.
I've also been part of several guilds focused around being mercenaries or just general adventurers, which is fine for a theme -- it functions, but it's a bit pedestrian. The biggest question is whether or not your guild adds something to the mix or not. If it's going to be almost exactly like another guild but with you in charge, you may want to just join that other guild. Being in charge isn't all that great.
Step 2: Get everyone on board
So you have your concept, and you presumably have at least one other person working with you. Great. Now your big goal should be, simply, to make sure that everyone is on board with the same ideas you have.
If you're picturing a guild in which your character is the absolute and unquestioned leader with everyone else just serving as a font of advice, you need to make sure that everyone agrees with having the guild work that way. If you're picturing a guild run by a council of founders, same deal. But don't assume ahead of time. Work out what people expect their individual voices and contributions to be.
As an aside, this is probably as good a place as any to point out that if players are officers, you should make their characters officers as well and acknowledge them as such. Leading a guild is a thankless job, and no one wants to be doing the legwork while being treated in-game as little more than a bystander. I've seen that done before, and it's not pretty.
If you and your fellows have some different ideas on this point, talk about it. In fact, even if you think you're all on the same page, talk about it. That won't prevent problems, but it will at least create some sort of precedent when they crop up.
Step 3: Run the guild
Yeah, that's it.
But what about rules?
Everyone is going to have rules that he thinks are important when it comes to roleplaying. You're going to have players who apply to the guild with very different ideas, and so the first impulse is to make a lot of rules to help codify what should be done. That way everyone will be put in the right mindset, right?
Wrong. There is absolutely no way to assure that everyone thinks the same way as you about roleplaying. None. The best you can do is try and get people around you who feel similarly, and you can find that out by interacting with the character before letting someone into the guild.
Rules about event attendance, event frequency, character dialogue, and the like only wind up making the game feel increasingly more like work. Work, you may remember, is the thing that you do just enough of to be done with it. The end goal of your guild should be that it fosters a fun environment, not that it forces people to play in specific fashions according to the whims of others. If someone doesn't like being around for events but does like roleplaying and makes for a great presence in guild chat, that person is an active contributor. If the reverse is true, same deal.
The best guilds I've been a part of have had zero roleplaying rules, but the community worked together and kept itself regulated. (Not to say that they've had no rules... but this isn't the pure guild column.) If you're relying on rules to force people into the shape you want, you're going about it the wrong way.
Want to tell me I'm full of it? Check on in with the comments down below or fling me a message to firstname.lastname@example.org. Next week, I'm dipping back into the profession well to discuss an old punchline: the Aristocrat.
Every Friday, Eliot Lefebvre fills a column up with excellent advice on investing money, writing award-winning novels, and being elected to public office. Then he removes all of that, and you're left with Storyboard, which focuses on roleplaying in MMOs. It won't help you get elected, but it will help you pretend you did.