I never understood the point/purpose of "microblogging." It's like making an entire post out of a throwaway comment. That's what I saw on mastodon, didn't choose to participate. Also found it was hard to find people I wanted to follow, and that it was flooded with porn I wasn't interested in and couldn't effectively filter.

The facetious answer is "post anything you want".

Realistically, you probably want some engagement, so post stuff relevant to your interests, and include hashtags so others will see.

Alternatively, if you want a little more structure, reply to posts you find interesting or have something to add to.

I tried Mastodon briefly, and I can safely say it isn't for me. I have a really hard time with the short posts, and the absolute lack of coherence between one post and the next. If you don't feel drawn to it, it may not be for you.

As a fresh-ish lemmite. It depends on what YOU are looking for out of it. A good example is "do I want to drive engagement for the sole reason of growing communities" in which case you just post to those communities. Leave softball comments on conversations. Easy stuff to prompt a followup comment "how does that work" "why does it work like that" even if you don't care, because it prompts a followup-comment. Posts that are easy like "today I learned X thing" even though you didn't, but if it's super popular and a lot of people knew about it, it drives big comment chains. This type of person is in every single comment section at least once. You see their names as OPs constantly. High post engagement rate (more engaging vs just clicking on the post then off the post) promotes things to the front page. Or at least higher than the bottom.

If you're looking for "honest" engagement then it's going to be more like "how often is my comment a worthwhile contribution?" In these instances it's follow-ups asking why X does a thing. Or answering someone else's question. You see this person rarely, and their comments are paragraphs. They could be right or wrong but they often appear to know what they're talking about. These people hang out in political subs (and other high controversy places) and drive conversation. Either they pick a side and defend it or are informing others how a system works.

Lastly is 2 opposite types. The ever-commenter who has 2k comments and no posts. They engage with EVERYONE as one of the above 2 types, even if it means they get downvoted or upvoted. This person will have a comment chain 35 comments long if people keep hitting Reply. Their counterpart is the ever-poster. They've got 2k posts and when you scroll they just the same post to 8 subs. Article about kid died in israel? They posted it in an Israel and Palestine sub, worldnews, news, a local news sub, politics, world politics, us politics, international politics, and noncredible defense. They post the same news article to every sub they can find. They rinse and repeat for each news article. This type of person rarely comments. These 2 people are the same but opposite sides of the spectrum.

Id say lemmy is more suitable for you than mastodon.