My advice to aspiring writers is my advice to me, and it's very difficult to follow: Write every day. In this, I fail. But it is something that I am trying to do routinely. Every successful writer I know, no matter the field she writes in, says you write more creatively and more quickly when you write daily.
"Like running, the more you do it, the better you get at it.” -Natalie Goldberg, Writing down the Bones