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.
Blog for the fun of it and show character. It is immaterial how many write about a particular subject, it is how you write the matters.
Use simple vocabulary. Important is to reach their hearts not testing their literary skills.