This is a good article that gives solid advice on some of the ways to develop a hardcore fan base. Of course, this is easier said than done, and reading a single article isn't going to magically get you there all on it's own.
The one tip that the author recommends that could actually bite you in the butt is the one about over delivering. I'm not suggesting that you be 'half ass' in the music you do or the way you interact with people - but there is a risk in trying to be too much to too many people and failing miserably. It's okay to over-deliver, but only in the context that it can be measured in some way to prove that it is actually adding value to your audience and also benefits your bottomline.
Otherwise, over delivering merely for the sake of over delivering can leave you overwhelmed and underpaid; and isn't that what most musicians are already grappling with in the music business today?
What's your take on this article?
How To Develop A Hardcore Fan Base