Most Common Prelim Mistakes?

Hey, I'm wondering: What are the most common mistakes graduate students make on the preliminary exams? I gather that one big problem is lack of clarity in the explication of theory. Is that the case? I just took a midterm which was designed to be a kind of dry run of the 2-hour, in-house prelim and my professor liked my essay because he thought it was clear and I used a lot of examples to explain what Burke was saying. What else besides using examples and clear, plain language can I do to pass the prelims? One person advised me not to talk about how I'm using theorist X in my work, but just to demonstrate my understanding of the theory.