Ask HN: How to get started with open source contribution?

What is the best approach to getting started with open source contribution? It feels a bit intimidating to think about where to start. First of all, how do you pick an area to contribute? Do you go with something that's related to your field of expertise? Is it even feasible to instead pick an area that you want to learn more about? Do you jump straight in and start fixing bugs to get started? What's the typical timeline by which you feel like you are being productive?