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.
After completing your post, read it with a fresh eye from the perspective of a reader to check if you enjoy it or if it needs changes.
Its not just good content that matters, presentation of post is very important too. Have attractive pictures, fonts etc to hook the readers.