命题作文要求就所给的作文题目进行写作。与其他作文相比，命题作文具有较大的自主性。因为同样的一个题目可以从不同的角度、用不同的文体来进行写作。例如“My Teacher”这个题目可以写成一篇记叙文，也可以写成一篇描写文。不管用什么文体，也不管从哪个方面来写，只要写出的`文章切题、流畅、条理清楚、语言正确就是一篇好文章。然而，这种较大的自主性也会使考生感到困难。因为在有限的30分钟之内，要形成提纲，并写成短文并不是件易事。这就要求考生在写命题作文时首先一定要审好题，要仔细分析题意，搞清楚题目所涉及的范围，确定文章的中心思想，切忌跑题。再者，要选择正确的文体。最后，要围绕文章的中心思想，将写作素材进行分析、归类并写好写作提纲，包括：引言句、主题句和结尾句。
［例1］Fake Commodities
Markets all over the country are swamped with fake and poor commodities. This has harmed greatly the state餾 interests and people餾 health. For example, false poison made in a factory not only can餿 kill mice, but also gives them immunity and makes them healthier.
The cause of this serious situation is that some enterprises only want to get benefit. What餾 more,some local governments, for the purpose of local protection, don餿 investigate such activities,on the contrary, they even support them. The judicial organs don餿 punish the offenders strictly.
We hold that the whole society should pay greater attention to these illegal activities, and these illegal activities should be punished according to the law. The leaders in charge should take effective measures to stop these harmful activities. Consumers should learn to protect their own interests, and not to buy fake commodities. In this way, we can at last wipe out fake commodities and leave no room for them.
作者把这个题目写成了一篇说明文。一开始先指出了假冒伪劣产品的危害。接下来分析了这一情况产生的原因，最后呼吁全社会都来关注这个问题。
［例2］Haste Makes Waste
There is an old Chinese saying,“Haste makes waste.”It was true in the past, and it is still true in many cases today.
Usually, if you act faster, you can reach your goals earlier. But it isn餿 always the case. If you emphasize only on speed but ignore the quality of your work, you will get the opposite result. Suppose you are preparing for your final examination. You have so many things to do that you don餿 have enough rest. You have to read and write continuously. The result is that your brain is less and less efficient, and the situation goes from bad to worse. All your efforts become fruitless. On the contrary, if your preparation follows a carefully worked out plan，your work will be effective. Consequently you will take part in the examination confidently.
Whatever you do, please remember the saying—Haste makes waste. If you can properly understand its meaning, you’ll benefit a lot from it.
作者在文章的开头通过重复作文的题目巧妙地点了题，接下来用具体的事例来说明这一众所周知的道理。