Define the central point of your paragraph. Express it as a sentence with two parts: the subject, which is what you are talking about, and the predicate, which is what you are saying about the subject. For example, the central point of your paragraph could be "Writers who write slowly tend to write poorly." This sentence will be your topic sentence.
Write as many supporting sentences as you need to clarify, expand and defend your topic sentence. While the length of a paragraph will depend on the scope and style of your writing, a good rule of thumb is that most non-dialogue paragraphs should contain three to five supporting sentences. If you need significantly more sentences to adequately support your point, consider dividing it into two or more paragraphs that each discuss a part of the topic.
Conclude your paragraph with a sentence that reiterates the main take-away you want to provide the reader in the paragraph. In shorter paragraphs (four sentences or fewer) you can leave this closing sentence out.
Re-read your paragraph and delete or modify any sentence that does not directly relate to the central point of the paragraph. To relate to the point of the paragraph, a sentence must deal with the same subject and support the same predicate, though not necessarily in the same words as the topic sentence.