Be sure the backstory enters the story at the time it’s essential to understand the plot, characters, or emotion. Not a minute too soon or too late. Sometimes backstory information has been added by you, the author, so that you can understand it. Cut it out and put it in a folder so that you can resurrect it, if you need it. If the reader doesn’t need to know it, cut it out.
Choose one word to replace phrases. Choose phrases to replace clauses. Change prepositional phrases like teacher at Fairbanks School to Fairbanks School teacher to adjective noun. (Darcy Pattison and Joe Hight both mention this in their articles listed below.)
Cut the adverbs. Replace them with strong verbs. (There are at least 20 sources that tell authors to do this.)
Don’t interrupt dialogue too many times with unnecessary actions. Cut the facial expressions and body gestures, like grimacing her face, raising her eyebrows, lighting his cigarette. Let the bigger actions speak for the characters. Make sure these actions are not ordinary. They are actions only a character like yours would do. Let them move the plot, highlight the character, and/or add emotional tension. Dialogue that is interrupted too many times with unnecessary actions like these might make a reader put your book down forever. Highlight the words in your text that interrupt the dialogue.
Rewrite the dialogue so it can be understood without tags of he said, she said.