Candidates must follow some strategy for scoring band 9 in reading as this part of the test is the one which tends to be more challenging for most of the candidates who sit for IELTS; which may be due to the fact that they are not aware of the challenges which they might need to overcome. Candidates are never advised to go directly for the passage, they can first go to the questions and then followed by skimming the passage instead of reading all the lines and they should exactly skim for keywords. They also adhere to the time frame as time constraint is the one which becomes a major challenge for many candidates which may be the result of not practicing regularly. Underling or highlighting can be done as it is not an offence in the IELTS exam. This can direct you or guide when you feel you are lost in the passage.
There are times where a candidate would feel that they are not aware of the meaning of the words and they might find difficult with the vocabulary of the reading passage. For this they could read the whole line and understand the word by knowing the meaning of the sentence. Check for spelling error and do not leave blank answers on the reading answer sheet. Capital font similar to listening answer sheet can be used in this as it may avoid errors. Coaching classes for the candidates to score band 9 in reading task for general and academic are given at Prestige institute.
References
https://ielts-up.com/reading/ielts-reading-tips.html
https://ieltsliz.com/how-i-scored-9-in-ielts-reading/