It is critical to always expand your vocabulary in English. If you know how to express an idea, that is obviously good, but if you can only express it in one way, then your communication will be limited.
It is very common in the IELTS listening and reading tests for some of the questions to centre around knowing synonyms.
For example, in the listening test you might see a question that asks about Ronald’s skill at playing the piano.
You could be asked if his skill EXCELLENT, AVERAGE or if he has NO SKILL?
On the audio you might hear that Ronald is a middling talent at the keyboards.
That question and answer involves three synonyms; skill – talent / piano – keyboards / average – middling. If your vocabulary is limited you will miss fairly easy questions.
Make sure that you are constantly working on your vocabulary.
Here are a few common synonyms. Check to see if you know them all.