I've learn from a couple of articles & tips here and there might help you to contribute to open source as well:
How to fix a bug in open source software: thorough article on how to triage open source software on several cases such as regression, stale issues, and not-a-bug.
CodeTriage: open source web app that helps you triaging by sending issues to your inbox, you can also set how many issues you are willing to handle each day and when.
A tip from Dan Abramov:
Open source tip: you’ll learn A LOT from taking a single project you actively use, “watching” it on GitHub and reading every issue and PR.
It won’t make a lot of sense at first but stick with it.