How to Write a Good Book

In comics, we talk about the silhouette test where each character's silhouette has to be distinct enough that you can tell exactly who it is just from silhouette. I think the analog for the silhouette test in fiction is to take a paragraph spoken by that character and line those paragraphs up. And if you can't tell that those are different people, then they're not different enough. This isn't something necessarily to do for every book, but it's something you can practice. If your characters are all individuals and all work well as individuals, as separate people, pull that off and... What world is your oyster?