What Makes a Good Sentence?
(in the context of a piece of creative writing)

• It says something new, or says something familiar in an engaging way. Perhaps it expresses a good idea succinctly.
• It makes the reader want to read on.
• It conveys the speaker’s motives and/or intentions.
• It is easy for the reader/listener to understand, but perhaps it has hidden meanings or ambiguities.
• It is easy/enjoyable to read/learn/speak.
• It communicates the voice of the writer.
• It sets the pace — short sentences speed things up.
• Perhaps it prompts further ideas in the writer’s mind.
• Perhaps it raises questions in the reader’s/listener’s mind or challenges his/her way of thinking.
• Perhaps it affects the reader’s/listener’s emotions.
• Perhaps it provides a cue for another character. Perhaps it poses a challenge to other characters.
• Perhaps it addresses/resolves an issue raised in a previous sentence.
• Perhaps it is short and "to the point".
• Perhaps it has a strong verb within the first few words.
• Perhaps it has few sub-clauses or none at all.
• It contains no unnecessary words.
• Perhaps it uses attractive/colourful words and/or sounds, perhaps enhancing the effect by using alliteration, metaphor, irony, etc.
• Perhaps it contains carefully chosen adjectives that fit the subject.
• It should be grammatically correct unless there is a good reason for incorrectness.
• Perhaps it uses unexpected words or unexpected combinations of words.
• Perhaps it uses memorable phraseology (inspirational, powerful, emotive, impactive, unexpected, etc)
• Perhaps it uses language appropriate to the time/place in which the action is set.
• Perhaps it uses rhythmic patterns and/or rhyme.
• Perhaps it evokes action and/or visual imagery.
• Perhaps it uses words/phrases/sounds that link it to other sentences in the same work or to external reference points.
• Perhaps it is amusing.

BUT RULES ARE MADE TO BE BROKEN…

• a character may be deliberately long-winded, pedantic, ungrammatical, etc.
• different styles of writing may be necessary to achieve appropriate differentiation/conflict between characters.
• special stylistic effects may be appropriate, for example to suggest the slow passage of time.