Practice those tasks in a large, already functional open source project. Try to shadow people who already do them. Very relevant link for libreoffice contributors of all kinds
Relevant more general guide (which doesn't look too out of date) here
Lastly I'll mention joining organizations adjacent to what you are already excited about working in. I do research code and joined an organization for data scientists in academia. They do regular training and events in things like UI design and documentation.
Haven't investigated it much, but I've been wondering if you could set your phone or something to transcribe audio and just talk out loud.