An essay should follow a basic structure that includes an introduction, several body paragraphs and a conclusion. The purpose of the body paragraphs is to provide information that supports the main idea or thesis of the essay as a whole. Each body paragraph should focus on a particular point you are making in support of the main idea. That point will then be supported by evidence --- details and examples you use to strengthen your explanation or argument. Furthermore, the body paragraph should stick to the same structure as the essay, with an introduction, supporting evidence and conclusion.
Determine the main point of your body paragraph, including what you are trying to explain and how it relates to the main idea of your essay. Once you have decided on your point, make sure you can support it with enough evidence to write a solid paragraph. If you can't support it with at least two or three sound examples, you should rethink the point of your paragraph.
Formulate an introductory sentence for your paragraph. Just as the overall essay must have an introductory paragraph, each body paragraph must contain a sentence that introduces the main point you are making in that paragraph. Try to summarize the point in a succinct way in one sentence, without going into specific detail.
Bring in the evidence you are using to support your main point. In several supporting sentences, you should give specific information that you feel highlights the point you are making. Be clear about how the evidence relates to your point, including how the examples illustrate the argument you make through your essay. As you move from one example to the next, use signal words and phrases such as "first," "in addition" and "finally" to clarify the organization of your ideas for the reader. These signal words indicate transitions in your writing and help lead the reader in the direction you want them to go.
Finish your body paragraph with a concluding sentence. This sentence should wrap up the point you have presented in the paragraph and serve as a transition into the idea of the next body paragraph. Begin the concluding sentence with a signal phrase such as "to conclude" or "in conclusion" to indicate to the reader that you are wrapping up the point you are making.
Read what you have written to check for clarity and fluency. Do the sentences of the paragraph fit the structure of introduction, support and conclusion? Does the paragraph make a strong overall point? Verify that the sentences are presented in an order that makes sense and contributes to the reader's understanding of your main idea.