Always let the picture do the talking! As a picture speaks a 1000 words.
Make good use of media (audio/ video/ embedded tweets, etc.) in your articles. It helps in grabbing the attention of the reader and supports your text.
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.