Niche market is a small subset of the total market. Lets say electronics. Thats a huge market. Now Television would a very small subset of the electronics, which you can call a nice. You can make it even smaller e.g. LCD Television.
Niche marketing is mainly used by affiliates. They take a single product or very small number of products within same category. Since the website on niche products is a small subset of products, they generally rank better.
As per marketing tricks I think same rules applies as like others.
Write articles and submit to article directories.
Have a blog dedicated to the niche.
Build links from any other sources.
Do on-page SEO.
Plus any other marketing tricks we use...