A good way to write main body paragraphs is this:
Start with an idea; Explain it in detail; Give an example
Here's an example of how I 'build' a paragraph using the above method:
A sense of competition is necessary for success in life, and should therefore be encouraged. Competition motivates children to get good grades at school or become better at sports, while adults compete to climb the career ladder. In a job interview, for example, candidates compete to show that they are the most qualified, hard-working and competent person for the post.
What's the topic of the paragraph above? What do you think the question was?