I don't believe in writer's block. I don't have the luxury to whine about being 'blocked" because I am making a living here. When I hear someone say that, I assume they are 1)lazy 2)fearful or lying to themselves about what they want. Writing is a job like any other. People at other jobs don't say, "I'm blocked today, I can't work." The reason people fail at writing as a career is because they indulge in ideas like "Writer's Block". To answer though, on days when I am having trouble getting it to flow, I write anyway. There are many exercises you can do to kick your brain into gear. Also, it's helpful to have two or three projects going at once, and switching between them.