Source.

Read enough SAT essays, and patterns begin to emerge. Some of them are good (I mostly still love seeing The Great Gatsby used as an example even though I’ve seen it a million times, as long as it’s appropriate for the prompt) and some not so much. Here’s a hodgepodge of common things you should or should not do, based on what I have seen people do over and over again. In my examples, I’ll pretend I’m writing an essay with the prompt from my recent contest.

• DO write a clear and concise intro that states your position, mentions your examples, and gets out of the way.
  When achievements are accomplished dishonestly, their value is diminished. Too often, people choose to cut corners to reach their goals, cheapening their success. Disgraced baseball star Barry Bonds and author James Frey are two examples of people who accomplished great things dishonestly, and whose achievements were diminished when their dishonesty came to light.
• DON’T ponder over the definitions of words, or different philosophies related to the subject. And please do not start your essay with “In life.” Just get to the point.
  In life, there are good achievements and bad achievements. When achievements are good they are achieved by honest means, but sometimes achievements are achieved dishonestly and are therefore bad. What is an achievement? It is when a goal is completed.
• DON’T claim that your examples are proof of anything. You are making an argument, not constructing a rigorous logical proof.
  The Great Gatsby and my personal experience prove that achievements are worthless if they are not accomplished honestly.
• DO choose examples that fit the prompt, and about which you are knowledgeable. 
  By the numbers, Barry Bonds is one of Major League Baseball’s all-time greats, but his dishonesty has cast a pall over his 21-year career. He holds the record for most home runs hit over a career, and the single-season home run record, which he set in 2001 when he hit a whopping 73. But when allegations surfaced that Bonds had taken performance enhancing drugs in the process of reaching these milestones, fans were appalled. Many called for the his exclusion from the Hall of Fame in Cooperstown, NY. He was dragged through protracted legal proceedings that lasted years and years; he barely avoided a prison sentence after he was convicted of obstruction of justice. Baseball experts generally agree that with his raw talent, Bonds would have been an elite player for many years. Because of his dishonesty and corner-cutting, though, Bonds’ name will forever be associated in baseball lore with dishonesty, not greatness.
• DON’T use hypothetical examples. Anyone can come up with an imaginary scenario that plays out in a way that supports an argument.
  If a gymnast lies about her age in order to compete the Olympics, and then wins a gold medal, and then an investigation shows that she was too young to compete, her accomplishment is meaningless.
• DON’T try out vocabulary words in your essay if you haven’t been using them successfully in real life. If you use a word wrong, it makes you look silly.
  Nobody will accolade her in the future because everyone will know that she has a past filled with lies.
• DON’T make too much up. You don’t need to know every single detail about your examples and it’s OK to fudge a minor detail or two, but if you’re completely in the dark about your example, you’re spending too much energy making up details and not enough energy crafting an argument. I get so much push back on this from students who have heard that they can’t be graded down for making things up, so I’m gonna hit you with the truth. Great works of literature with robust plots and salient themes were carefully crafted over months, if not years. If you’re so arrogant that you think it’s easy for you to come up with a realistic sounding plot of a completely new book in 25 minutes, I won’t argue with you. But I will have no pity on you when your grader is not impressed.
  In the book The Science Test, by Clayford Shuckins, the main character, Matt, has to pass a science test. He doesn’t think he will be able to pass it without cheating, so he asks his friend Ellen if she will let him copy. When the results come out, and Ellen and Matt have the same grade despite the fact that Ellen worked hard and Matt did not, Ellen resents Matt and reports his cheating to the teacher. Matt ends up with a zero and his parents are disappointed.
• DO be as specific as you can about everything. Specificity is probably what I harp on the most when I work with students on their essays. See my Barry Bonds paragraph above for a bunch of specific details, including number of home runs, what records he holds, how long his career was, what crime he was convicted of, etc.
• DO conclude your essay succinctly and without fanfare.
  Both Barry Bonds and James Frey were natural talents who might have achieved what they did without dishonesty, but the reputations of both men have been sullied because they did not accomplish their great feats honestly. Achievements are diminished if they are accomplished dishonestly.
• DON’T cut an example paragraph short in order to write a conclusion if you’re running out of time. You are graded on what you put on the page, not what you leave out, and you’ll do better to make good points about your examples than you will repeating yourself in a conclusion.
• DON’T start your conclusion by writing “In conclusion.” I hate that.
• DON’T make overly grandiose claims about what you have accomplished in your essay.
  As the stories of James Frey and Barry Bonds prove, it is never OK to lie, and those who do will always have their reputations destroyed.