Rule: At the beginning of each paragraph, you need to let your reader know what point the paragraph will make. Because the purpose of your paragraph won't be a simple restatement of plot, your topic sentence should NOT be a statement of plot. Each topic sentence should help move the essay toward proving its thesis statement. A topic sentence at the beginning of a paragraph suggests neither more nor less than the whole subject of the paragraph, in a brief, general way, without mentioning details.
Examples:
Bad topic sentence: One time, Holden goes skating with Sally.
Better topic sentence: Holden's inability to maintain a polite conversation manifests again while he's skating with Sally.
Bad topic sentence: Emilia takes Desdemona's handkerchief.
Better topic sentence: Emilia's taking of Desdemona's handkerchief allows much of Iago's mischief to happen.
Practice revising plot statements into strong topic sentences:
Resources for further explanations of how to write strong topic sentences:
Purdue OWL's Topic Sentences
Letter Pile's How to Write a Great Topic Sentence