Many students waste time writing long introductions and conclusions. These two paragraphs should be short and simple; a long, complex introduction or conclusion will not give you a high score.
Just make your introductions and conclusions quick and concise, and spend your time writing really good main body paragraphs.
Here's my introduction and conclusion for the topic of my last two writing lessons:
There are various benefits and drawbacks of books, radio and television as ways to convey information. In my view, television is definitely the most effective of these three media.
In conclusion, although books, radio and television each have their advantages and disadvantages, it seems to me that the impact of television is greater.