I have made some small contributions or tried to, to some open source projects in the past and I must say, Servo has been the most welcoming and most beginner friendly. The team has clearly made it a priority and it shows.

Personally for me the hardest part has been finding easy issues. While the Servo team does a great job of creating them, there's a lot of people vying for them. And then, even harder, progressing from these to bigger harder issues, which is where I'm still at.