Pick a topic it can be a general topic, or theme. You can get ideas from other bloggers. The goal is to make your blog unique and something that is totally your own.
When you find the topic that you enjoy writing about, have plenty to say on the subject.
What you decide to write about determines what type of readers you will attract and how you make money from those readers.
Most mommy bloggers like to write about they family, kids, daily frustrations.
You can add your own personality into the tone of your blog posts you can create a blog using a very popular topic and make it your own.