Man, if you want to work on, rework, or fine tune your writing muscles just get a blog without any type of expectations. It just makes it easier when you have to go back and do it for real.
You can kind of write at will, get ideas down, experiment. Short or long as you want when it comes. Take as little or much time as you want to. Not so demanding as a Twitter or Facebook. Public practice for your rawest thought and form.
