I am interested to know why you write those comments, tweets or posts. I am specially curious about heavy writers commenting at least once a week.
What I've discovered so far, is I enjoy answering Ask HN questions the most. So I keep an eye on the new Ask HN submissions, and comment when I see something where I might have something to say. I especially like when I can share from a place of personal experience and help someone else out there in the world.