You should write about what you know but then the things that you know can become so familiar that it is difficult to see them through fresh eyes. When you write about the things around you, your sense of understanding comes through in the writing. I have been taking ideas from people from childhood and situations that have arisen. They have given the stories a feeling of nostalgia, I think. At least from my point of view. I don't know if this will show in the writing or not.