To avoid repetitive sentence beginnings, keep an eye out for multiple sentences in a row beginning with the same word. Most often, repetitive sentence beginnings start with:
a pronoun (he, she, I, they, it, her, his)
a character name
an article (a, the)
a conjunction (but, and)
a conjunctive adverb (then).
That kind of repetitive sentence structure leads to a monotonous rhythm, causing readers’ attention to wander. It’s important to vary the structure of your sentences. Try mixing it up — start some sentences with words other than names or pronouns.
There are no hard-and-fast rules about how many repetitions are too many, but generally, two times in a row is fine; three times might be too much.
The same is true for paragraph beginnings. Keep an eye on how many paragraphs in a row start with the same word, and if more than two start with the same one, switch it up.