Write what you know. Do I know a lot about murder? Not really, but I've studied a lot of police procedure and crimes. A mass murder took place within twenty miles of where I live and from that, I learned a lot.
Writing murder, I've written about things I know and have incorporated them into my novels; such as One Last Bet. I trained and drove race horses, so what the reader takes in is a lot of true information about the sport itself.
I write to keep a reader interested by keeping the story moving. I don't like to read dull stories and I don't write a dull story.