Know when to stop lecturing. Certain presentations–especially in advanced or upper-division classes or seminars–can require you to present some material, then lead a discussion. Be sure to attentively listen to any comments or questions your classmates might raise before starting on your answer. And in a discussion period, never lecture (only discuss), and be sure to answer exactly the question asked (don't offer up more canned–but irrelevant–material). In many classes, how you discuss is as important as how you present.