Topic Sentence: This is a general statement that expresses the main idea/topic of your paragraph, and that the other sentences support or explain. The topic sentence has two main parts: the subject-- what the paragraph is about, and the focus-- what the paragraph is going to say about the subject.
Ex. Personal computers (subject) have improved our lives tremendously (focus).
Supporting sentence #1: This is where you give your first supporting fact, detail, and/or example.
Ex. First, computers have made it easier for students to complete homework and projects using different software applications like Word, Excel, and PowerPoint.
Supporting sentence #2: This is where you give your second supporting fact, detail, and/or example.
Ex. Second, people can communicate faster with friends and family using Outlook Express for E-mail or Instant Messenger software.
Supporting sentence #3: This is where you give your third supporting fact, detail, and/or example.
Ex. Finally, business people can get more work done, because they can use a computer from home, on a plane, or any other location.
Concluding sentence: The closing sentence restates the main idea of your paragraph.
Ex. As a result, computers have made our lives easier.
Sources: Harris, Jeanette and Ann Moseley. "Expressing Main Ideas as Topic Sentences." CONTEXTS: WRITING AND READING. 2nd ed. Boston: Houghton-Mifflin, 1989: 46.