Recently (April) I took a workshop with bestseller L.A. Banks. She spoke on a great many topics (her energy is boundless) but one was on world building. Not just a paranormal or alternate history world, but building your fictional world.
Characters, neighborhoods, work environments, they're all part of your world and as sch part of what yo need to build. Is your Hero white from a rough poor neighborhood? Better get those slang words and accents right then. How about former gang member? Better brush up on that, too.
Now this doesn't mean you have to go to a neighborhood with a gang or spend time driving around with a camera. Research is available in so many ways to our networked writers. Take advantage of it! Ask around, someone always knows someone.
Use this to your advantage - the more authentic the setting the more 'real' the story will be to both you and your readers.