The best things to write about are the things you have lived, loved, or worked with. How did you grow up? Anything fun or nasty about where you lived? I could probably write a book about our neighborhood, and at least a chapter on our neighborhood bully. Did you go to public school, private, or home school? What may have been "just home or just school" to you, may be interesting reading to someone who grew up elsewhere. Or even just a pleasant reminder to a fellow catholic school survivor. (of which I was one. Those nuns could be good aim with an eraser, I'll tell you!)

Anyway, hope that helps some.