In short, paragraphs should have the same structure as whole sections. A reader should be able to grasp the thrust of your argument by reading only the first couple of sentences of each paragraph. Write short, declarative sentences. Avoid the passive voice. Write from an outline.
Outlines are major aids to coherence and readability.
In fact your class papers will be read by teachers who probably know something about your topic, but they want to see how you would lay out your argument for folks who don't. For more advice on writing, see William Strunk Jr., and E. B. White, The Elements of Style , 3d ed. Two heads are better than one, and giving and receiving comments are important skills. Take care to turn in a neat, clean paper. Run your spellchecker.