The sage advice in business, as well as in book publishing, is to generalize:

Serve as many people as possible. Be as a broad as possible. Be excellent at everything. Make everyone happy.

I disagree, and strongly.

If you specialize, you can become excellent at what you do. If you try to become excellent at everything, you probably won’t even get (just) good at anything.

Focus on what you’re terrific at. Or, at least, focus on the one area that you want to become terrific at. After you’ve done that, select another area.

But I’d argue that it’s impossible to become excellent at many things, all at once.

Be a specialist.