When a writer feels misunderstood in a critique group setting, and starts explaining what he or she was getting at, the response is often, “That's brilliant, what you just said, right there, that's the line that should be there on the page...”
If I need a sentence that perfectly defines one of my fictional characters, I sometimes imagine I'm having a conversation with a friend of mine who's isn't present, and immediately come out with the line I want. The problem with this being that my daughter for some reason finds it embarrassing when we're walking down the street and I talk to people who aren't there...
Here's an idea I found in Alan Cooper's The Inmates Are Running the Asylum: Why High Tech Products Drive Us Crazy and How to Restore the Sanity. Cooper says when designing a user interface for a software product, the trick to making it user-friendly is to imagine a specific user, a fictive individual with clearly-defined gender, interests, class background, and so on. Then while designing the interface, imagine the experience of using the interface from the point of view of this imaginary person.
We evolved to be good at communicating to individuals, not to demographics. So conceiving of your demographic as an individual might help you access the part of your brain that's good at communicating. What happens if, while writing fiction, you bear in mind a target reader who is not an abstraction, but as fully fleshed out as a character in a novel?
This connects to why I feel justified in posting comments on my own blog entries. Sometimes other people's comments help push me towards the thought I didn't quite manage to encapsulate in the original post.