Can't speak for the OP, but as we do the same thing, figured I'd contribute our answer.

We're not great at "sales", so it's been completely organic growth and word-of-mouth. I went to a lot of events and meetups for startups, and talked to people about what they were doing and what we do. I've also done a lot of open source development, including working on the Rails core team and building our own projects like Dynatable.js.

This took a lot of time to cultivate a sales pipeline. The company was just me for the first 4 years, occasionally sub-contracting as needed. Then over the next 6 years, we grew to 6 people, and are currently in the process of finding a developer-consultant to join as our 7th.