Something that may not be thought of often by writers is pacing. It is a difficult thing to work on as you write only because it can sometimes only be felt when reading the book as a whole. However, it is a very important aspect of a story making any great story unbearable to read because how fast or slow the story progresses. The length of a book can make it even more difficult to get the pacing right with more time spent perhaps in exposition. A good way to tell if a book has good pacing is if a reader "flies through it," or "can't put it down."
