Since you cannot submit an entire paper, think carefully about the problem you are having which will allow you to get help. What is your paper's purpose? Does your thesis statement and introduction work with your body paragraphs and conclusion? What are the main points of your essay and could you list them? Do your body paragraphs have topic sentences and are there details, examples and other evidence which offer proof about your thesis? Is your essay unified in its entirety and help your reader follow the path you are developing about your topic? Think about your audience. Does your paper's tone fit your thesis and audience? How smoothly does your paper flow? Look at the transitions in your paper. Are there jumps where you assume knowledge by your reader or skip leading them with your ideas? Rewriting really means revisioning what you want to say or prove with your paper. I hope this helps.