In my experience, attitudes towards repetition vary greatly among the writing community, ranging from those who seem neither to notice nor particularly care about it, to others who are keenly aware of every instance of repetition and check their work over and over again to comb out all offending words.
As a general rule, too much repetition is a bad thing, because it can make the writing seem dull and lacking in imagination, particularly in the world of fiction. If a writer describes a scene where the flowers are beautiful, the weather is beautiful, and the woman standing looking at it all is wearing a beautiful dress, the reader is unlikely to be hooked and eager to read on. Perhaps the flowers could be pretty, the weather perfect, and the dress elegant. Inserting synonyms here and there would be an improvement, but it may be better still to go a step further and vary not just the words themselves, but also to adjust the sentence forms as well.
So, the above scene could go from:
The woman wore a beautiful green dress as she looked at the scene in front of her. The brightly-coloured flowers at her feet were beautiful and the weather was beautiful, too.
The woman wore an elegant green dress as she looked at the scene in front of her. The brightly-coloured flowers at her feet were pretty, and the weather was perfect for the time of year.
…and then to:
The woman stood gazing at the scene in front of her, the deep green of her elegant dress enhancing the blue of her eyes. On the ground near her feet, pretty daisies and marigolds opened their petals wide to welcome the sunshine on this perfect spring morning.
Another point to bear in mind when avoiding repetition, is to make sure that the synonym used fits the tone of the rest of the writing. Care must be taken to select the right term, otherwise the end result may not be quite what the writer intended. For example, a thesaurus may list ‘beauteous’ as a synonym for ‘beautiful’, but that is a much more literary, archaic term which would not fit very well into a modern story. Similarly, ‘cute’ or ‘bonny’ are informal terms and would only work in certain colloquial contexts.
It is perhaps a good idea to avoid using a term more than once within a couple of paragraphs, although there are exceptions to the rule. Sometimes, repetition can be used deliberately, for emphasis or to create a particular effect. Also, smaller, common words such as ‘the’, ‘a’, ‘of’, ‘in’, ‘and’, etc., can be used more frequently, otherwise it would be difficult to write anything coherent at all. Occasionally, though, finding an appropriate alternative can be hard, especially if the original term is quite specific. In these cases, I would argue that it might be better to simply repeat the word, rather than substitute it with something that is a bad fit and might spoil the tone of the narrative. The occasional repeated word is quite harmless (many of the best writers do it), and as long as the writing flows naturally, it may well go unnoticed by the reader.
(Thank you to Lizzie Hagon for the lovely lettering!)