Engagement with the Hacker News community. An euphemism for "the next best thing to free ads" :)
* traffic (which is nice, but not super sticky)
* the comments (which I've found to be insightful and useful in showing both flaws in my arguments as well as additional areas for research/writing)
* the follow-on traffic, as people share it in newsletters, slacks, facebook groups, twitter, etc, etc
The best way to engage with the HN community? To be part of the community (comment, share interesting things that are not your own, etc) :).