The main purpose of your conclusion is to summarize the main points of your essay. The means you are going to repeat your 2 positive points and 2 negative points. For example, if my essay is about the advantages and disadvantages of banning smoking, I might say:

"In conclusion, there are many arguments for and against banning smoking. On the one hand, research shows that smoking is bad for your health and is anti-social. However, on the other hand, smokers should have the freedom to choose whether or not they want to smoke. Not only that, but the tax from cigarettes gets spent in many important areas such as health and education..."

A conclusion like this will help the reader/teacher follow your arguments and will increase your chances of getting a good result for your essay.