It typically includes a topic sentence that gives the main point of the paragraph, followed by additional sentences that expand, qualify, analyze, provide examples, or explain the idea. Often they end with summary sentences. All good paragraphs are unified, complete, and coherent. Unity means that the paragraph has a single focus. Completeness means that the subject of the paragraph is adequately developed so that the reader is satisfied and not left with vague impressions and unanswered questions.
Coherence means that all of the sentences in the paragraph are related to one another.
Handbook for Writers. I have put sections on unity, completeness, and coherence on reserve at the library. These sections contain detailed information and provide examples. For reasons of copyright, I could not scan them to put on the Web. You might wish to refer to Wayne Gregory's On Line Writing Guide at Tokyo International University.