People often ask me about using 'complex' sentences and 'difficult' words or grammatical structures. Here's an example question that someone asked me:
I can see you did not use any long and complex initial sentences to begin your paragraphs. I wonder if sentences like this are useful: "In recent years, …. has never failed to attract people’s attention and spark controversy over the potential impacts of this trend on individuals."
My answer is that examiners are not impressed by this kind of sentence. Instead of judging it as 'complex', they are more likely to judge it as 'memorised'.
Here's my tip: instead of trying to impress the examiner with big words or memorised phrases, try to impress him/her by answering the question really well. Plan some good ideas before you start writing, then do your best to express them in a natural way and without making too many mistakes.