I've never joined a guild because I'm terribly shy and meeting new people absolutely terrifies me. (I'm a disaster during open house at work every year but I'm working on it.) Maybe have a person or two (someone who is warm and friendly in a non-invasive way) adopt a new person and make them welcome, sit with them, etc. until they got to know some people. Also, if you have a website for your guild, make sure the tone of your site is welcoming. There's a big guild near where I live but I've never checked it out because the tone of their website is not very friendly.
BTW -- The church I've been going to has a quilting ministry on Wednesday nights and I'm going to try to go this week. Wish me luck as I try to meet new people without terror!