You don't have to be writing a novel or formal essays to improve your writing. Writing every day about whichever topics you like is enough to exercise the writing muscle.
Now here's one thing Brandon, , and I agree on. In fact, Gabriel once emailed me near verbatim what Brandon wrote above within an email exchange of us lamenting our lack of progress with fiction writing.
From writing consistently -- although I haven't done so in public the entire time like Brandon -- I've likewise noticed an uptick in writing quality. Quality not only refers to the output but my overall experience of it. Writing is now more enjoyable, and many things I used to consider menial about it are now intrinsically satisfying. I no longer longer always feel the rush to just get my ideas out there and hit the send/publish button. I actually like sitting down with my ideas and statements and seeing how they might be received.
Finally this quality increase appears in unexpected places. I never thought I'd enjoy writing emails as much as I do now. I never thought that I'd feel a deep sense of flow while writing notes on how to implement some user interaction in code. And I kid you not I'm already stoked about write 'instructions/documentation' for this writing community.
So how can writing consistently made the act become so enjoyable? I think it comes from an increased awareness of the craft. I think many people -- including myself -- do themselves a disservice by shoe-horning themselves as X or Y or Z writer. Because then they feel like they need to write a certain way and when it doesn't flow within that way they become frustrated.
When you write consistently -- the right way* -- you begin to not self-imagine yourself as a writer who should be producing X,Y,orZ and is failing to do so, but instead simply observe and suspend judgment. And this is when the actual message can flow out through you. From not trying to write a certain way, I've been so surprised with all the different places and means from which I've found appreciation for writing.
*I'll write about the right way in another post.