https://github.com/topics/good-first-issue
Any issue marked "good first issue" should be good for someone new to the project to tackle. The link I posted, the 2nd entry is a repo with docs on how to contribute to projects.
My best recommendation would be to find a project that is written in languages you're familiar with and maybe even is on a subject you're familiar with (e.g. data management, audio transformation, business logic, statistics, whatever) and just dive in.
Shohreh Aghdashlo is definitely my first pick.