1) Have a blog

2) write something (do not finish!)

3) release it (minimally, stick it on github or something similar)

4) blog about it (and post the blog entry somewhere where people will see it, aka here)

5) guilt will drive you to make it better

6) work on the project and blog more about it

7) Either people will get interested, you'll start getting links or it won't go anywhere

8) decide whether to continue it or start the cycle over again at step one with a new project

If you do this a few times, I guarantee that you'll have a blog with readership and a better idea of what people want/wnat to work on.