Rule: Avoid repetition. If you can express the same idea in fewer words, you should. If you use the same word more than once in your essay, you should find synonyms and/or pronouns (as long as they're clear).
Examples:
Wrong: If you don't want to go and be there instead of here, then you should come home to your house.
Better: If you don't want to be elsewhere, you should come home.
Wrong: He wanted to go to the new school, but the school was far away and he didn't know a lot of people at that school, which was a scary school.
Better: He wanted to attend the new school, but it was far away, unfamiliar, and scary to him.
Practice eliminating repetition from these sentences:
John came into civilization from a place where he'd heard about civilization but hadn't ever seen civilization.
John Proctor admits his affair to the court, but Elizabeth tries to save him in court because she doesn't know what he has admitted even though she knows that he had the affair before he goes to court.
Around the same time when Taylor is going on her journey to find herself and to leave her home and everything she has known up until this point in her life is around the same time that she finds Turtle and then starts her journey.
Judy and Noel demonstrate generosity. They give presents because they're really giving people. In fact, they often give gifts to people; that's just who they are.
Resources for further explanation on how to avoid repetition:
University of Queensland's Structural Repetition
The Writer's Dig's 5 Ways to Deal with Word Repetition
Shmoop's How to Avoid Repetition
You might enjoy playing this game to practice reducing unnecessary verbiage: Brevity