Do you have a tendency to go off topic when writing? Read the last paragraph, then the paragraph before it and gradually go up the page doing the same with each paragraph. Consider if your writing is less cohesive when read this way, or if it still easy to understand. If it becomes hard to follow, then this is a sign that you might want to edit out parts. The reader should in theory be able to understand the message from top to bottom and bottom to top. I find this method useful when setting up arguments and structuring explanations of particular topics.