The first, and most obvious, was writing ability. Blogging is mainly a written medium, and the most successful bloggers can turn in some sparkling prose.
I can’t figure out a better way to phrase the second, so I’ll call it the ability to push people’s buttons. Some of the best bloggers seem to deliberately aim for topics and ways of expressing themselves that get people going. Some rile people up; others make them laugh. The best are rarely working on a purely intellectual level.
The third was reliability. It doesn’t matter how brilliant your post is if I’m only seeing one post every few months. Consistent posting goes a long way in establishing credibility,
Finally, expert bloggers are community building. The best bloggers link out to other blogs, leave comments, get comment threads going, and support fellow bloggers, not just spruik their own.
Additional, 18 August 2012: This blog post at Pharyngula is on the mark:
I’ve been at it for about ten years, with my share of controversy, and none of it really contributes to long-term growth: not Expelled, not the cracker, not every little sudden surge from Reddit and Fark and Digg. Those give little bursts of attention from people who weren’t interested in your blog in the first place; they visit to see the source of all the commotion, and then they leave.
What makes a blog grow is 1) regular updates, 2) consistent themes, 3) maintaining the attention of other blogs out there, 4) cultivation of an interactive readership that adds value to your blog, and 5) time (slow steady growth is best, and it can’t by definition happen overnight). Probably also good writing, but I wouldn’t know much about that, and I’ve also seen some gloriously well-written blogs that idle along with light traffic because they ignore my top 5 suggestions.
Substantial overlap in our lists. Interesting.
I think my biggest problem with this blog is maintaining consistency (Myers’s second point). I think this is why Better Posters is a more successful venture.