The thesaurus is not your friend. To write clearly, choose your vocabulary wisely and stick with your choice. This advice goes against what most people were taught in high school: "Vary your vocabulary! Vary your sentence structure!"
Many beginning writers mistakenly believe that using different random words will make their texts more interesting, when in practice it only makes their texts more confusing.
Clearly define vocabulary
When you are writing an informative text, clearly define the vocabulary you are using and use it consistently each time. This conscious consistency is especially important for key words but can be applied to any vocabulary choice. If you change the word you use, you are signaling to the reader that you intend to change the meaning. Don't use a different word if you actually mean the same thing.
Do you have a model, a method or a theory?
If you have people in your research, will you call them participants? patients? people? individuals?
Will your idea be called a strategy, a technique or a principle?
Readers expect to be shown consistency: using different words when you mean the same thing will not entertain the reader; it will only cause them to wonder what they missed and what in the world you are talking about now.
Why does this work?
Synonyms are not interchangeable. They each have different definitions, connotations, and situations they are best used in.
The novelist Tahereh Mafi said it best:
Synonyms know each other like old colleagues, like a set of friends who’ve seen the world together. They swap stories, reminisce about their origins and forget that though they are similar, they are entirely different, and though they share a certain set of attributes, one can never be the other. Because a quiet night is not the same as a silent one, a firm voice is not the same as a steady one, and a bright light is not the same as a brilliant one-- because the way they wedge themselves into a sentence changes everything.
They are not the same.
How important is consistency?
On a scale of 1-10, it's an 8: pretty important! Writing about your research is not the time to show off your extensive vocabulary. Choose the best word to get your point across and stick with it. Are you having trouble maintaining consistency? Ask for help!