A proper paragraph should begin with a topic sentence. The topic sentence, much like the thesis statement in an essay, sets up the argument or introduces the subject that the paragraph will be about. A topic sentence can be analytical, such as "The Civil War was an important moment in American history," or more personal and reflective, such as "My summer in France was the highlight of my year." In all cases, the topic sentence should tell the reader exactly what the subject of the paragraph will be.
After a topic sentence has been written, it needs supporting evidence that will back it up. This comes in the form of the paragraph's body, which usually consists of a few sentences giving further explanation or providing evidence. In the Civil War paragraph, the body could include statistics that demonstrate the devastation of the war, or the social repercussions and racial divisions that followed. In the France example, the body might detail memorable events that took place during the writer's summer vacation.
A paragraph needs to be rounded off nicely with a conclusion to maintain a coherent structure. The concluding sentence can do one of many things. It can restate the topic sentence in a new way. It can also summarize the evidence presented in the body, reminding the reader of its importance. In a more personal or narrative paragraph, the concluding sentence can place the paragraph's topic into a larger context, or reflect on possible future consequences.
No matter how good the topic sentence, body and conclusion are, a paragraph's structure also depends on the flow of its language and sentences. One way to achieve flow is by using transitional words between sentences. After a topic sentence, you might begin a sentence with the word "firstly" to introduce the first piece of evidence. For a contradictory statement in the body, use the word "however" or "nonetheless" to begin a sentence. Give flow to the conclusion with the words "overall" or "in the end."