A paragraph is the smallest unit of prose composition. It may be defined as a group of sentences relating to a single topic.
Every form of prose composition (e.g. letters, essays, stories) should be divided into paragraphs. A paragraph may be long or short. There are no rules regarding the size of a paragraph.
Tips on writing paragraphs
Unity of thought
A sentence deals with just one thought. In the same way, a paragraph should deal with only one central idea. The ideas need to be developed in a logical order. They must flow neatly between the paragraphs.
Use linking words
Use linking words to achieve the effect of unbroken continuity. For example, the words hence, so, therefore, but, and, or and then will connect the sentences and make the paragraph a well-knit whole. Use expressions like on the other hand, on the contrary, nevertheless, but, yet and still to contrast ideas or present alternatives.
The first sentence is the key sentence in a paragraph. It should introduce the central topic. The last sentence should round off the idea expressed in the paragraph.
Variety
Use varied sentence patterns in the sentence. There should be both long and short sentences. This rule of variety also applies to the size of the paragraphs. For example, put a short paragraph after a long one. It will afford variety and relief to the eye as well as to the mind.