From SEO Diva 

There is a very good article on The Art of Niche Keyword Analysis for Social Media Marketing at SMMWhiz. It's a little advanced, but if you want to target your niche, especially for social media, it's an excellent guide.

Steps include:

1. Preparing for Analysis
2. Analyzing Competition
3. Buzz Tracking
4. Removal
5. Keyword Clustering

The author, Ashwin Ramesh, says:

Whenever you engage in Niche Determination, make sure that the niche’s you select are relevant to the product or concept you are selling.

You cannot run a site about cakes and target niches involving rocket propulsion systems just because more people are searching for the latter.

It is important to stay bang on target and finally give some value to the user and place user experience over monetization and search engine visibility.