The paragraph
Make the paragraph the unit of composition. Paragraphs are single ideas that start with the topic or a transition (word, phrase or sentence giving direction) and have a beginning, a middle and an end. According to Fowler, ‘The paragraph is essentially a unit of thought, not of length; it must be homogeneous in subject matter and sequential in treatment.’
Use basic structure: The first sentence states topic; the middle sentence explains or illustrates; the final sentence wraps up, closes.
Give new topics new paragraphs.
Ask yourself this question: Will division ease comprehension?
Example:
Transitions
Transitions are an important tool for clarity and continuity: and, but, while, or, then, such as, on the other hand, however, next, therefore, for example, finally, furthermore, consequently, in addition, nevertheless, meanwhile, accordingly, thus. Use them. You must make certain that the relation between one sentence and the next, and one paragraph and the next, is clear. Often it will be clear without an explicit transition, but do not take too much for granted; relationships between sentences may not be as clear to your readers as they are to you.
Transition words indicate passing of time, addition, contrast or opposition, comparison or similarity, concession or admission, sequence, result and summary. Vary their placement in the sentence in order to avoid repetitive syntax.
A word of warning: over-elaborate introductions kill the purpose of the transition. Rather than coax the reader on, you cut off the flow: ‘In the next section of this report, it is my intention to deal with the problem of noise pollution’ versus ‘The next problem is noise pollution’.