Find a problem first. Then try to implement a solution using your language of choice (Node in this case). An example could be: "I want to create a service that parses books and lists the most frequently words used. A step further would be to have the user enter a longer piece of text and analyzes it (http://www.online-utility.org/text/analyzer.jsp)"

Another example is "I want to create a service that auto-corrects text that users enter."

Try to find something that would make your own life easier. Chances are that other people are having the same problem.

Shameless plug. Hopefully you get some ideas out of it: http://jairampatel.com/projects.html