There are many ways to make a market research, but today I will tell you how you can do this by Internet.

1. First you need to define your target market. After this you can use tools like Google Trends or Google Market Finder to find all appropriate keywords for your market.
2. At this step you need to make a lot of searches on Google and copy any website to an excel document (we will use later to sort competitors by size).
3. For every website in your excel you can search for Alexa rank (this tell you how visited is a specific website) and put in your table. Now you can filter this competitors by size.
4. BONUS: You can skip steps 2 and 3 if you use TheWebMiner.