So you've got goals for your guild, and you've been working very hard toward recruiting new members. One of your next big challenges is keeping them around. Turn over is a plague among beginning and middle-tier guilds. Sure, guild dynamics like raid rules and bank privileges play into who stays and who goes from your guild, but it is more important to help make someone feel a part of the team.
Think about your own experiences in joining guilds. Have you ever been in one where nobody seemed to talk to you, except to ask if you could make them a flask? What about the guild that shifts their raid times, and doesn't make it clear to all members. WoW is a social world and new guildies are subject to the same anomic forces that someone might feel during their first few weeks at a new job.
First things first. Let your new guildies in on your expectations. It's helpful to have guild policies posted permanently on a website so that they can quickly learn what to do and what not to do. Be firm, fair and consistent with enforcing these rules for new guildies as well as established guild members. For example, loot systems can be daunting at first. Have a clear explanation and be prepared to answer questions. You may consider appointing an established member to helping your rookies learn the ropes.