The idea is that the first draft is basically an unloading of all the ideas in your head. You don't stop, you just get out the beginning, middle and end. The developmental edit is what turns your manuscript into a novel. What does this edit involve?
First off, you need to add all the fluff that makes a story jump off the page. Things like sensory details, metaphors and similes. Suppose I wrote about a birthday party in my first draft. I mention the cake and the balloons. During the developmental edit is where I make sure to have included details like chocolate cake with vanilla icing, a description of the colorful balloons and perhaps the sound of them popping. You make sure that you are showing, not telling. It is during this edit that I flesh out my characters, give them a stronger voice and personality. It is also when I make sure that my characters aren't flat, but change and grow.
Another big part of this process is looking for holes. You want to make sure the "magic object" your character found in chapter four actually comes up again later in the book. You need to make sure your plot and sub plot(s) go in the intended direction and actually make sense. This is where you make sure that the underlying story is what it needs to be and that all the other elements line up. As you read through your work for this edit it is a good time to make sure that your premise works and that the story is believable.
When these things are done then it is time to move on to the grammar and sentence structures.- Dorine