Let me explain about IELTS reading with regards to comprehending the passage and how to deal with long passages that are difficult to understand. The advice below is for the academic reading passages and also passage 3 of the GT paper, which is also a long passage.
How do I remember everything I have read?
The answer is – you don’t. IELTS reading is not about remembering what you have read or what each paragraph contains.
How can I understand everything if the passage is long and difficult?
The answer is – you don’t. IELTS reading is not about understanding everything. It is about locating answers.
When you first get your reading passage, you should skim read it. This means you cast your eyes over the passage to get to know the general topic and content as well as to see the general layout of the passage. This should take about 2 minutes. You are not aiming to understand it, you just want to see what the passage is about before you tackle the questions.
After you skim read the passage, you go straight to the questions. Pay attention to what type of question type it is and remember your techniques and tips for that particular question type. Find a key word or information in the question to help you locate the answer. You scan the passage by casting your eyes over the words to locate the key information from the question. This should be done with speed to spot a word or piece of information rather than understand each sentence. Once you locate the place in the passage that contains the answer, you read the sentences before and after to find your answer. This means you only need to understand those few sentences. Then you move to the next question and do the same. You don’t need to understand the whole passage at all.