You must do keyword research to determine the potential of the topic that you will use. Many ways to get a good keyword. Slow way is to use free tools and you can find many free keyword research tool by simply entering "free keyword tool" in the Google search box. 

Pay tool will provide faster results. Micro Niche Finder and Market Samurai are a two-keyword tools that give the best results. Next post will discuss about Micro Niche Finder and Market Samurai Review. Stay tune :)