Treat writing as a job. Be disciplined. Lots of writers get a bit OCD-ish about this. Graham Greene famously wrote 500 words a day. Jean Plaidy managed 5,000 before lunch, then spent the afternoon answering fan mail. My minimum is 1,000 words a day – which is sometimes easy to achieve, and is sometimes, frankly, like shitting a brick, but I will make myself stay at my desk until I've got there, because I know that by doing that I am inching the book forward. Those 1,000 words might well be rubbish–they often are. But then, it is always easier to return to rubbish words at a later date and make them better.