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.
Keep your posts simple! Do not try to impress anyone. be yourself! Visit other blogs which might interest you, take part in conversations or simply put your two cents for others to read and follow you back to your blog.
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.