The best advise I can offer you about blogging is:
1. Write about something that really interests you, something you are passionate about.
2. Write about something you are learning.
Of course, it makes sense to concentrate on what you are passionate about. You have been into this topic probably for many years. May be from early school days.
Therefore, you are an expert on your topic. That's great! We all want to read about the experiences of an expert. It's more interesting, and more informative.
People who write about their passion capture your imagination, and often touch your own feelings very deeply. So you feel connected. You feel like you have had similar experiences in your own life.
You find it interesting and worthwhile to listen to an expert. You are learning something valuable, because you believe this person is genuine.
My personal field of interest, my obsession is Internet marketing. You can find loads and loads of information about this topic online.
But, you won't find out what I know unless you listen to me.
Why should you listen to me?
Because I have a unique take on what it takes to be successful in Internet marketing.
One of the most important things I've learned is the need to FOCUS. You have to focus on one niche, one narrow area, one activity, where you can concentrate all your efforts till you achieve the results you want.
You may say you already knew this. BUT, you don't now the details of how to implement it successfully.
Many people know about the need to focus, but hardly anyone actually practices this.
The second thing is to write about something new you are exploring.
You are already an expert in the field you are passionate about, and that's great.
But I am especially intrigued about what new things, what new techniques you've uncovered that you're now exploring.
These are the things that the competition most likely has not learned about yet. These are the new "secrets" of the trade, which a master like you, is now uncovering and testing.
That's the leading edge, and that's what I am most excited to hear and learn about.
Once I determine that you have tested your new insights, and proven them to work, I will be right there to learn what you have discovered.
And if I have to pay you to get your new discoveries, that's OK. You deserve to get paid for your new knowledge, and I am happy to pay you.
Because I know you are an expert in your field, I know I will get true value for my money.
I also know that I will save countless hours that it would take me to discover what you have.
And since I do not have your level of expertise, chances are I may never discover these things on my own.
Therefore, if you are trying to figure out what to blog about, write about what you are an expert on, AND write about the new discoveries you're exploring.