The topic sentence may come anywhere in the paragraph, though most logically and in most cases it is the first sentence. This immediately tells readers what is coming, and leaves them in no doubt about the overall controlling idea. In a very long paragraph, the initial topic sentence may even be restated or given a more significant emphasis in its conclusion. Use Paragraphs are used to divide a long piece of writing into separate sections. Each of these sections should deal with one issue, or one topic in a sequence.
Paragraphs are a device to create firm structure in writing.
They can also be used to give rhythm, variety, and pace to writing. If in doubt, keep your paragraphs shorter, rather than longer.