Words and phrases to avoid in IELTS essays.
The essay writing section of IELTS is formal, this is the same for academic writing task 1 reports, so you must use the right register. You could lose marks in vocabulary or grammar if you are writing in an informal way, using idioms, or using memorised stock phrases.
In IELTS general writing task 1, you will sometimes get an ‘informal’ letter to write, so obviously in that specific case you will write the letter in an informal register.
You may not lose a band score if you are doing just one of these things below, but if you are making a combination of errors then it could be the cause of being stuck at band 6 or 6.5.