By reviewing existing clients for the industry that is most profitable, most enjoyable and most systematized, then naming it publicly. A specialism is usually discovered in the current client base rather than chosen from scratch, and it can be stated without turning other work away.
A specialism is usually discovered rather than chosen, and it is normally already visible in the existing client base.
Look for the industry that is simultaneously:
That overlap is your niche. It is rarely the industry you expected.
Naming it publicly does not turn other work away. This is the fear that stops most firms specializing. In practice a contractor-focused firm still gets restaurant inquiries. What changes is who arrives first and what they expect to pay.
The commercial argument is straightforward: a specialist is not compared directly with generalists on price. Nobody shops a specialist against three others. They shop a generalist against three others.
Specialization also improves search visibility, since a page naming an industry and a city can rank for searches a general accounting page cannot compete for.
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