I have discussed the importance of knowing a word’s connotations and denotations, as well as avoiding the repetition of specific words or phrases. However, you cannot simply take an oft-repeated word, look it up in a thesaurus, and substitute something else in its place without checking that it is a grammatical fit.
For example, the words research and study can be considered synonyms, and indeed, they are quite similar. For example, each can be used as a noun or a verb. However, this does not mean you can use them interchangeably.
She carried out a study about the effects of pollution.
Her research about the effects of pollution won an award.
In this particular instance, study can be substituted for research in the second sentence … but research cannot take the place of study in the first because research does not take the article “a”. She can carry out a study, or carry out research, but she CANNOT carry out a research.
Another thing to be aware of is English idioms. For example, you can have a piece of work to do, but you CANNOT have a piece of job. If English is not your first language, it is useful to have someone else review your work to ensure that words are used correctly. Even if English is your native tongue, a fresh pair of eyes is always helpful!