Now, I don't think you need me to tell you that when you're building your world, and even more importantly when you're setting your story in a real world setting, you should really pay attention to the details.
Remember that Will Smith movie where it starts out he's chasing an alien through the streets of New York, was it Men in Black? And he jumps off the overpass that rings around Grand Central Station. And two blocks later they're running passed the Gugenheim. That's like 40 blocks! I know, I know, it could be they were going for time-lapse, but it still bothered me.
Well, it's the same in your novel. Even if you invented the fictional town your story is set in. It can't take someone twenty minutes to bike across town at one point in your story, then later they run over quickly to warn someone about something. A lake has to be where a lake is, for the whole story.
One of my favorite books from the last year or so is The Language of Flowers, by Vanessa Diffendough. The story is amazing, but what is so impressive is the perfection with which she paints San Francisco. There is a community garden on a corner where she says it is. I can even picture exactly where her character walks in a public park and finds flowers and trees and bushes specifically placed. Now, yeah, if you don't know San Francisco, it doesn't matter. But since I do, the book is that much more magical.
So even if you're creating a completely fictional town, I strongly urge you to draw it out in detail in your mind. Know where every house, every store is.
Now, let's talk about what your characters know, and what they don't know. If Mary wasn't there for a conversation between John and Sue, Mary can't know what they talked about. She can't know what was divulged to whom by whom. And once they know something, they know it. I just read a book where something was explained to a character in the beginning. Then later in the book, he doesn't know it again and he's told the same thing again. Now he could have forgotten, but no, it's obvious the author forgot the character had been told something earlier. It's just not clean writing. If you're telling a story, keep your facts straight! And actually, you have to keep everyone's facts straight! What all your characters know, what they're aware of, what they think, how they feel about someone or something. Particularly if you're writing a mystery!!!
