Presentation is as important as good content, Have attractive pictures, fonts etc. on your blog to hook the reader.
Write regularly, neither too often nor too rarely. Two to three blogs a week is a good frequency to maintain.
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.