If you want to find a niche in your writing, follow your dreams and passion. It could be something you love doing in your spare time, or something which you enjoy in life, or even some thrilling experience you've had which people are interested to read about.
This brings me back to a nasty auto accident I went through when I was driving from Wisconsin to Toronto during my university days in the US.
Funny you should be asking me this question. I am still finding a nice niche in which to start my freelancing act as a translator, writer and marketing consultant.
Hope this gives you some inspiration.