First guild guide, if you don't agree with it don't bite my head off.
STEP UNO: GUILD CHARTER
First, you want to name your guild in a way players will be interested in it. It can be humorous, have roleplay value, pertain to its theme, etc. For example, I run a guild named Raid A Holics (derived from Noggaholics) in which we commence raid instances and raid minor towns (almost pulled off a stormwind, died on our way to Cathedral). Choose one you like is the most important.
STEP DOS: RECRUITMENT
Now, recruiting is the blood of a guild, it keeps a constant flow of members. I am in a guild (<The Shadow Of Time>) with 191 members. How to get that many, you say? Excellent recruiting. You want to make your macro appealing in most senses. Include level boundaries, what instances you are capable of doing, how many members you have so far, and what you plan to do later. It is ALWAYS better if you provide info to someone who may be interested. End-game guilds are some of the most popular, especially on PvP realms. Roleplay guilds also recruit fairly well, although it isn't too often a roleplay guild grows large (more than 150 members). Try and word your macro to be polite and inviting. You also want your classes to be as diverse as possible.(at least five of each class is a good idea) You can't pull of an MC if your guild is filled with mages and warlocks.
STEP TRES: MANAGEMENT
There used to be a guild named Blackmarsh Raiders. They had 400+ members, with at least twenty online a day. And it fell apart. Why? The guild leader couldn't hold it together. Managing a large guild can be difficult. Your first order of business should be electing some co-leaders. These people should be people you trust, so you may leave various matters in their hands. They should be at least as active as you are, or at least enough to handle things in your stead. There are some difficult decisions, such as when to promote, if they deserve it or not, etc. A good idea is to host a promotion day, so that people have a heads up to contribute to the guild for a chance to be promoted. Take it easy, and if someone is dissatisfied with your guild, do your best to adapt to keep them in. Every member is precious.
STEP QUATRE: KEEPING AND ACTIVE AND SUCCESSFUL GUILD (conclusion)
You want your members to be happy, and you want to recruit more and keep a steady flow coming into the guild. For this reason, be sure to host several appealing events (e.g. a festival, raids, movies, etc.) and mention them in your recruitment. Don't be too strict, be flexible, and don't let your temper flare. Your members are the guild's life blood and you want to keep them in. Another way to do this is to let them piece in ideas for a guild tabard, if you get a little bit of everybody it should be great.
Use these tips to create a successful guild, hopefully one you will enjoy. And speaking of enjoy...ENJOY!