Grammar - Depending on the language you use, blogging just makes it imperative that you are reasonably good with your grammar skills and proficiency if not a master. Remember your audience is a mix of both; the ones who are experts and the ones who are not.
Follow up on comments you wrote on posts. Continue the conversation. Bloggers enjoy engaging with their readers.
Engage readers with well-researched and creative blog posts. At the end of it ask questions or feedback from them.