A good paragraph should have a clear internal structure with an opening, development and ending. Each paragraph should deal with one idea or aspect of an idea, and it should be clear to the reader what this main idea is.
This idea is usually shown in the topic sentence (see next section). It is important to remember that paragraphs in different parts of an article or essay have different purposes, and may be very different. However, most paragraphs tend to have 3 parts: an opening sentence (or sentences), development of ideas/information, and an ending/closing sentence.