Great question! I can relate to this from my own personal experience.
Back in 2010 I started my marketing company, and we worked with everyone from mom & pop restaurants, to professional services (lawyers, chiropractors, financial advisors, etc.), to non-profits, to thought-leaders.
We had lots of different projects, and enjoyed the diversity and novelty of our clients, but we were not strategic with who we brought on as clients. Basically anyone that was willing to pay us, we brought on as a client. And at the beginning, you need to do that to survive. But, you also have to know that will not scale, and you will not build a brand that way. It was a complete nightmare from a management and growth side...
Strategies, tools, and tactics that worked well in one industry, were against regulations in another, or didn't fit that business model, etc.
The goal of a personal brand is to build a magnet, a reputation in the marketplace, that attract clients to you, rather than you having to chase clients, and take whatever type of client will pay you.
People pay a premium for people who specialize.
The medical space is a perfect example of this.
Your general doctor, or urgent care physician serves a purpose, but they don't make heart surgeon, or brain surgeon money. And, people aren't flying across the country or world to see the top urgent care physician/doc.
So it depends on what your goals and ambitions are to determine what steps to take for your personal brand.
The basics are:
Find a growing trend/industry. Plant your flag. Specialize your skillset, team and processes to where you can get predictable, and repeatable results for your customers and clients. Build a company and a brand by creating raving customers, and being the go-to solution in that industry.
Hope that helps!
Michael R. Hunter