First of all, a really deep niche can only be served online. Only in the full universe of the internet will there be enough interest to sustain a deep niche business. That’s the whole Long Tail thing.

Therefore, deep niche service is primarily an SEO function.
And any good SEO strategy starts with keyword research.

Let’s say you want to start a niche informational product.
Before you fall in love with an idea write down all of your possible areas of expertise/interest.

Expand them (use a mindmap, perhaps) into as many smaller categories as possible.
Think of words and phrases someone might search for if they needed information about each topic.
Use a thesaurus, and Google Sets to find more ideas for topics and words.

Then hop over to the Keyword Tool. Check out small groups of related keywords in batches. Save data from interesting results in a spreadsheet.

Look at the top performers. Any keyword phrase or set of related phrases that gets over 10,000 searches a month is worth looking into. Go to regular Google search and see what the organic leaders are for each of the phrases.

Poke around the sites of the top four or five results. Look at the source code. Look at the design.
Does it seem like a total accident that this site is at the top?
Or is it obvious that someone has a vested monetary interest in being there?
How hard would it be to get into first page ranking?
Is this site what a searcher would be hoping to find?

Obviously, what you are looking for is an under-served market. Once you’ve identified that, buy a keyword-rich domain name, set up a blog, and start writing.
And start creating a product of some sort.

If you do it right, you’ll start drawing worthwhile traffic about the same time you have a product ready to sell.

Niche served.

This post is part of the Brogan 100.
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