What's worked for me:

Find an interesting question.

Investigate it.

See where that leads.

In particular:

- What are the foundations of that question?

- What are the implicit assumptions or beliefs? Are those valid?

- What references or sources are frequently cited or quoted? Are those valid?

- What questions, concepts, or sources are studiously ignored or deprecated? Why? Are those valid or invalid?

- What are the dimensions / what is the internal structure of the question? What are its elements, dynamics, and/or relationships? Where do those lead?

- What are the issues encountered in trying to realise solutions, mitigations, or models of the problem? Working in idea-space is one thing, working in instance-space quite another. ("In theory, the same, in practice, different.")

- What new questions emerge? Rinse, wash, repeat.

My problem isn't that I don't have enough to write about, it's that I've far too much I'd like to address, and am looking for a structure and system that fits this.

If you're not at this stage, simply writing, regularly, is good practice. Things you have to say may not seem to be meaningful, and perhaps never will be. More likely though you'll discover a through-thread in the problems and approaches to those problems you're drawn to, though it may take years or decades to discover this.

Writing is a great way of documenting your sources, discoveries, thought process, and evolution of understanding or approaches. It took me several decades before I'd read my past writing without constantly crigning. I still frequently revise or correct older essays (even years old), and HN's very limited edit window is a constant frustration (as are Mastodon and Diaspora's complete lack of re-editability). Your own git-managed blog provides both for editability and a history of those edits.

I've found the process of exploring writing and research methods (tending strongly toward cross-referenced systems: index cards, Zettelkasten, POIC, Wikis) to be fascinating in its own right. Often to the exclusion of writing itself ;-)

Capabilities of a particular platform also matter. If you're writing-as-marketing (a frequent mode), there's one set of tools which may matter, generally fairly well addressed. If you're writing-as-dialectic, exploring ideas or seeking a better understanding of truth, there are others, less-well supported. I find that comprehensive search, thematic organisation (a very good tagging system), and, if feedback is supported (comments, etc.), an exceptionally effective, efficient, and low-cognitive-overhead moderation system matters a lot, as well as the ability to structure posts sufficiently to the needs of expression. A reasonably robust semantic structure (emphasis, lists, sections, tables, figure/images, footnotes, possibly equations) can really matter, and many solutions support this poorly (or require much wrestling).

Content-appropriate themes and styling also matter, with a narrow band between "not enough" and "too much". Again, many solutions support this poorly.

Finally, there's the ability to move your content elsewhere, when (not if) your current platform becomes inadequate or inappropriate, for whatever reason. Something I've come to discover is inevitable.

Another interesting discovery has been writing on microblogging sites. My preference is Mastodon, though Twitter is similar. I'd realised that Mastodon's default 500 character toot length is roughly the same as an index card, which means I can post in threads of roughly index-card-sized chunks. I know this is somewhat annoying for readers, but as a writer, the immediacy of feedback, at roughly paragraph-level granularity, to elements of a longer essay, is invaluable. There's also the notion of publishing in chunks, and committing yourself to a direction publicly, whilst still composing. Several of my longer "tootstorms" really just started as an aside or observation and grew on me.

A key distinction between writing and conversation is that in a conversation, you get immediate feedback. In writing, you commit yourself to a much longer exposition without having a good idea how your audience will respond. (Even speechwriting or presentations are like this, though in delivery you can adapt to audience response.) Microblogging has at least the possibility of bringing writing closer to the conversational mode, which is interesting.