Are you using email to communicate with your audience? You probably should be. One of the most effective ways of communicating with a group of people is with an email list, even in today's Twitter and Facebook culture. In order for your list to be effective, it first needs to exist, and then you'd like for it to grow. Just how do you let people know about it and get more email subscribers?
Typically, you'll have a sign up form somewhere on your website, possibly on your Facebook page and you might get some referrals from current subscribers. In order to get more attention for their email list, there are plenty of folks employing pop-ups and overlays to get people to sign up for their list. You may even already subscribe to this site's email updates, but you get the pop-up, just the same. I'm not sure this method is the best way to do that.