I highly recommend reading the book "Blue Ocean Strategy" that is the best and simplest way to map out the landscape of the marketplace and identify opportunities or methods of differentiation.

If you don't have time to read the book I'm sure there videos out there summarizing and explaining the core principles.

We walk our clients through the Blue Ocean Strategy mapping and simply follow the process in the book, and it's quite powerful and valuable.

I don't know of any other process that VISUALLY REVEALS the opportunity in your market.

The other way is to look at your past clients:

Is there a majority of clients that you worked with that fall into a niche demographic?

Is there a subset of your clients that you enjoyed working with more so than others?

Is there an area of your expertise that you're more passionate about that would lead you to dive deeper into a niche? (IE: career transition, executives in healthcare, women in tech startups, Female executives for 7-figure startups, etc.)

Hope this info helps!