The easiest way to write a short, effective conclusion is to paraphrase what you wrote in your introduction. Let's try this with the introduction I wrote last week.
It is true that the top sports people earn incredibly high salaries. Although reasons can be given to justify this, I personally believe that sports stars should be paid much less.
Conclusion (loosely paraphrasing the introduction)
In conclusion, I do not accept the argument that sports professionals deserve to be paid so much more than people who do other important jobs.
Notice that I wrote "loosely paraphrasing" (I paraphrased the overall idea, rather than word for word).