Add your personality - If you are writing on a particular topic, there are a number of people who will be writing on the same topic. So you need to add that specialty to your blog to make it look different and to allow your readers to take away something that the others are not offering.
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.
Blogging is more about you writing your experiences than what readers want to read. To get the right audience, follow your heart and write what you actually go through.