In any piece of writing, there are many possible ways to write any sentence correctly, but usually, of those correct versions, one or two will sound better than others. A writer who can pick out those versions and can use them frequently will have a strong sense of sentence fluency. This does not mean creating longer sentences, but means using long sentences when they would be best and short sentences when they would suit better. It means creating a sense of rhythm with the sentences and a flow that the reader finds enjoyable to follow along. Good sentence fluency stands out when a piece of writing is read aloud.