Unfortunately, most people do not read a great deal, nor do they continue on to graduate school to study writing, where you will learn this in a direct manner. I don't know where these high school teachers get this nonsense about synonyms, but if you want to be a bad writer, I strongly recommend you use nothing but synonyms and never repeat words.
One of the things you should do as a writing consultant is to help your client understand what good writing looks like. If they insist that they don't want repetitions, it is your job as a writing consultant to help them understand why this is wrong.
There are several reasons why avoiding repetition is wrong.
- Repetition Creates Meaning: Repeated words are perceived as meaningful. I am not talking about words like "the" and "a," of course, but rather theme words like "repetition" and "meaning."
- Repetition Creates Rhythms: There are a variety of ways to create rhythms, from the regular beats of formal poetry to repeated words. The latter are sometimes more complex, but they create patterns all the same. And when you have patterns, your brains pick up those patterns and remember those patterns. If you want people to remember your texts, you need repetition.
- Search Engines Pick Up Repeated Words: Search engines search for number of precise words used. They do not pick up synonyms. Thus, for any online text, it is particularly important that you have important words repeated.