What motivates you as a writer? Fame? Money? Glory? We all hope for those to some extent, but what really gets you to sit down and put words on paper?
If your anything like me it's pressure. Unless there's something that makes me feel a real need I just can't bring myself to do it. I think that's why deadlines came into existence, to get people like me to do it.
So what use is this to us? Well like I said before the best way to improve is to write, a lot. You can't always be writing for publication. Sometimes you just need to write for practice. But how do you motivate yourself if you're writing for something as nebulous as practice?
Set your own deadline. Make it something real, something with consequence. When you write to publish the consequence is simple. You don't get published. Do something for yourself to make it real. Whether the outcome is positive or negative depends on you. Personally I'm not much for self flagellation. I bribe myself with a pack of trading cards for a game I enjoy. It works for me.
Now just figure out what works for you and get to it. The clock's ticking.