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.
For folks looking for new guilds, it's probably best to research the guild a bit before donning a tabard. Some guilds request that you limit trolling on the forums or in trade chat -- if you're prone to such behavior, consider yourself warned. There may be a period of time before you become a full member, and may have restricted privileges during an introductory time.
It's also helpful to have alts and crafters marked in guild notes to help new guild members figure out who's who. I've been running my main with a new guild. Fortunately, as a tank, I can kind of sit idly by and listen in vent to get a who's who. It might be harder on a healer when the raid leader calls out a command including someone's first name -- that you haven't been formerly introduced to. It's kind of a balance between maintaining a friendly atmosphere with the established guildies and helping the new folks figure out who they're supposed to be healing.
Most importantly, let your new guildies know that you are aware of their presence. Help them feel welcome. It only takes a moment to type "Hey, how goes it?" when they sign on. You may be able to get some company for dungeons or quests. Established guilds can seem quite cliquish. I understand that sometimes your guild is "like family," but if you're recruiting, you probably want people to join your in-game clan.
One person's bad experience with joining your guild could mean good or poor publicity on your server depending on how you treat them. You could drive someone away by being standoffish and eventually develop a reputation for snubbing new folks. If their experiences are positive, your recruits might want to bring along their friends, or have something good to say when they are asked about their new guild.
As corny as it sounds, think about how you feel when you join a new guild. Treat others the way that you would like to be treated and you stand a better chance of keeping that new tank or healer around.
WoW.com offers a plethora of information on guild leadership and guild membership. Be sure to check out Scott Andrew's Weekly Column Officer's Quarters and keep an eye on the community with Mike Schramm's Guildwatch.