I answered this in a little more detail further down the page, but the short version is that I didn't really have a customer acquisition strategy. I just had a little overlap from my blogging and a product that I wanted to build. The rest was pretty basic. Do things and tell people. By talking about it, I was able to reach a fair amount of people who were interested and start from there.
In terms of a competitive market, I really just kind of went the opposite direction from the established options out there. The truth is that those other apps were and are great for some teams doing large complex software development projects, but there was a whole other group of smaller teams that didn't need all of the advanced features that those big players offered. I thought the world need something between a todo list and those options, so I tried to fill in the gap.