Competition always makes me more productive. I’ve written my best stories when they were for contests among friends. I knew if I didn’t turn in something good, I wouldn’t live it down, so I’d meet the deadline no matter what.
By writing enemy I mean someone you want to be better than, someone you want to defeat. Someone on your skill level that you can struggle against in a friendly way. Who can write more words in an hour/day/week? Who can get a story into x magazine first? Who can write the best story as judged by some other group of friends?
I find when I’m writing for other people, and not just myself (as is so often the case with unknown writers) that I’m much more productive. And if you’re not able to find anyone to beg you for more writing because they want to read it, I’m sure you can find another writer to compete against!
Try it, it will improve your productivity!