Attracting contributors to your Open Source project

So you've put your repo on github, you've shared the link on Twitter, Hacker News, wherever else you want, and you wait patiently for the pull requests, issues and stars to roll in from this incredible Open Source community you've heard so much about. Nothing happens. You share it again, still nothing.

Let's take a look at projects that are very welcoming to new contributors, and we'll try and emulate what they do in our own projects.