I'm working on growing our little guild. I've met with some success. I don't spam trade chat to advertise our guild bank, vent, website or or smokin' hot tabard (all of which we have). I like to get to know people a bit before I bring them into the fold. The best way that I know how to do that is to run instances with them.
Since we're small, I PUG a lot, so I'm introduced to many players. I'm looking for folks that are both good at what they do and would be a good fit for what we've established. I've found that many times people pug because even though they're in a guild they can't seem to get the assistance that they need. I find that some are actively looking for a change and others just generally enjoy the experience grouping with my comrades.