We use the music/publishing analogy here often, so for this post, I'm going to talk about audience development in terms of something I know painfully well: being an independent musician.
As a musician, it can be difficult to get a recording published, book a show, and basically anything else outside of creating the material itself (which has its own set of challenges). Same for authors, right? In many cases, publishers and promoters will want to have a clear understanding of how big your audience is. If you have to convince them of how big it is, things quickly become challenging.
Being in this position can mean three things to publishers and promoters:
1. You're just starting out.
2. Your material has a niche market.
3. What you're doing isn't as interesting to others as it is to you.
If point 1 or 2 apply to you, there's a great opportunity to advance. If you're just starting out, the world is your oyster, and you need to start looking at people and places that align with your topic - both physically and from an interest perspective. Barbara Cave Henricks has a great post on dealing with this from an author's perspective.
If your material has a niche market, there are ways you can try to open it up a bit. Yours is a dedicated group, who also have a wide range of interests. Connect with them as much as possible to get a good understanding of their diversity. Then communicate with them with this information in the fold. Your audience will grow, and they will have done the work for you. This concept has been championed by folks like Seth Godin, Jack Mitchell, et al.
If what you're doing isn't as interesting to others as it is to you, take one step back from your idea and consider why others might not be as excited. Do you have specific criticism? Good. Apply it and see how things change. If not, try coming up with different approaches to your work that still feels right to you. Sometimes the "first draft" isn't the best, and with more revision, even you will become more excited about it. If not, maybe it's time to find a new idea.
Once you beef up the audience a bit, you'll find the publishers and promoters will become more receptive because they'll have something solid to work with. Then, each and every accomplishment you do make, becomes fuel for more.
It takes A LOT of work. Whether you're a new author, or you've been around forever, the second you start coasting will allow the thousands of others to gain market share. Enjoy the ride.