When preparing for an exam, it's helpful to take something you've already written and attempt to re-write it. In doing this, work towards combing two sentences into one. This will create a single powerful 'punchy' sentence that has more quality content.. After we have already written something once, it is always more powerful if we write it again.
Example: ORIGINAL Nick Carraway guides the audience on how to feel. When Jordan is about to get into the taxi persuading him to allow Gatsby to meet Daisy for tea. A warmly lit Nick says "The modesty of it.". This shows the audience that Gatsby, for all his showmanship, is really quite endearing and Nick likes him, so we like him too.
REDRAFT As Nick Carraway and Jordan are catching a taxi, the character becomes a moral compass to the audience. Luhrmann uses warm lighting on Nick's face and his soft tone of voice creates a pause from the showmanship of the city lights to indicate Gatsby's truly generous nature as Carraway states "The modesty of it.". The audience becomes as endeared towards Gatsby as Nick has.
NOTE: The second paragraph has more flow and detail.