Here are my 'main body' paragraphs for last week's question. Notice that it's possible to put advantages and disadvantages together in the same paragraph. Also, you need to be careful not to write too much!
Advantages / disadvantages of books:
The main advantage of books is that they are usually considered to be reliable sources of information. People tend to refer to books when they want to research a subject in depth, and for this reason they continue to play an important role in education. On the other hand, books quickly go out of date, and therefore they are not the best medium for communicating news stories.
Advantages / disadvantages of radio:
Radio is a much more effective medium than books for the communication of up-to-date information. We can listen to news broadcasts about events as they happen, and a key benefit of radio is that we can listen to it while doing other activities, such as driving or working. The main drawback of radio, when compared to books or television, is that there is no visual element; we cannot see what the broadcaster is describing.
Advantages / disadvantages of TV, and my opinion:
In my opinion, television is the most effective of these three media because it brings us closer to reality than a book or radio programme ever can. For example, we can watch events as they take place on the other side of the world, or we can see the body language of a politician who is being interviewed. The disadvantages of television are that programmes tend to be short and interrupted by advertisements, meaning that information is presented in limited depth.