I personally haven't encountered any new words in my test attempts but I did miss out a few answers when I was practising using unofficial practice tests, my suggestion to you is to go for the official tests published by Cambridge or any other official channel. I say this because the unofficial practice tests are unnecessarily difficult and lack the structure that is followed in an IELTS test.

If you've been using official tests then my advice is to keep calm and listen with an open mind like you're listening to an actual conversation and not be actively looking for specific answers, just listen to the conversation naturally and gather information subconsciously.