Transparent Startups looks awesome.

One way is to build projects for an audience that you either know or can reach. That might be something local in your city, HN, etc.

Another thing to consider is what your goal is — do you want regular users, paid users, newsletter signups, just feedback, etc?

There's also a regularly recommended book called Traction [1] that you might find useful. One of the authors is the founder of DuckDuckGo.

[1]: http://tractionbook.com/