When Is the Writing "Done"?
Rule #4: Ask your best readers if the body of the paper is done.
One of the hardest decisions writers have to make, after "how and when to start," is the opposite of that choice, "how and when to stop." If we had all the time in the world, the writing could go on forever in a ceaseless cycle of adding new evidence or replacing weak evidence with better evidence, improving the logic of our reasoning, fine-tuning paragraph order and transition, refining word choice, etc. In real life, writing must end because it has to do its job of communicating something in order to matter to its readers as well as to its writers. Writing needs to do things, to change the world. To do that, writing must be given to readers, and their reactions (if you can predict them) will tell you if the writing is done.
Think strategically about how to predict your best readers' responses to the paper. What questions will they probably ask, and what answers have you given them? Have you presented an original thesis supported by enough accurate information of an appropriate sort in an order that will make sense to them? The nearer you get to saying "yes" to those questions, the nearer the paper is to being done.
If you value your grade, do not attempt to predict your best readers' behaviors on your own. Talk to Writing Center tutors and ask them to read the paper one last time with certain specific questions in mind (e.g., "have I included enough specific examples or are there too many?"; "does the introduction tell enough or too much?"; "are the paragraph transitions working?"). Ask a member of the class whose judgment you trust to exchange papers with you for a final reading. If you can persuade the sharper members of your class, you may be able to persuade the instructor.
Have you asked the instructor if s/he will accept preliminary drafts for advice? Never neglect this most obvious way to learn what your best readers want from your writing. Try to remember that even your instructors are not, ultimately, your best readers. When your long apprenticeship is over and you send your writing to your editors or employers or clients or constituents, they will be your best readers. Your instructors are attempting to simulate their needs and reactions to the best of their abilities.
Now that the body of the paper is finished, you know some things about it that you didn't know when you first began writing. The shape of the whole paper now can be creatively modeled into its most effective form, and you can use that process to write guidance for your readers in the last stage of editing before proofreading for mechanics and spelling.