Don’t use a word more than once in a sentence.

This is a very basic writing tip anyone can give you. Don’t use the same word more than once in a sentence (or even a paragraph) — unless that is the point.

This generally happens for one of the following reasons:

For what we think are important words. “She was decisive about her decision”. While you might think of this as reiteration, it’s just odd.

When we use the word as part of a jargon or add a modifier. “If you are more of a book-person, there are several books and free resources available on the internet.”

In conditional sentences. “Unless they trouble you, you need to remain silent” — in this the two you’s follow each other, a little jarring to the ear. However, “If you’re afraid, you can stay home” is all right. Because even though ‘you’ appears twice, it isn’t awkward.

Prepositions in idioms. This rule doesn’t apply to articles and most prepositions. But think of this sentence, “He is the most clued in in the area”. Avoid this kind of preposition repetition.

The thing with repetitions is that it’s not technically wrong. It’s just ugly. Try alternatives.