When you are reading a short passage for the first time, read it carefully. A short passage is one that is only seven or eight lines long. You can retain all of the main ideas and remember where particular things are mentioned from one careful reading. Hence, you do not want to waste time reading this passage twice.
Besides wasting time, another bad consequence of reading a short passage very carelessly the first time is that it may leave you with some false impressions of what you have read. Wrong ideas can get stuck in your head from a careless reading. Then it will be more difficult to get the correct answer.
For long passages, look ahead to see what is being asked. Take a look at the "stem" of the question, the sentence that precedes the answer choices. And look at the kinds of choices that are being offered. Sometimes reading passages are long but the questions are asking only for particular details. In that case, you can often skim a long passage to find the particular detail.
Keep forging ahead. Do not get bogged down if there is a word or sentence you do not understand. You may get the main idea without knowing the individual word or sentence. Sometimes you can sense the meaning of the word from the context. Sometimes the word or sentence may not be the basis of any question. If there is some idea you need to answer a question but do not understand, read it one more time. If you still do not understand it, move on. You can come back to this question later if you have more time at the end of the test.
Picture what you read. Try to form a picture in your mind as you read. Schoolbooks used to teach reading contain many pictures because pictures aid comprehension. When reading material without pictures, it will aid your comprehension if you use your imagination to picture in your mind what you are reading. Read as if you were a professional illustrator who has been hired to do an illustration for the passage.
Ask yourself questions as you read. When you finish reading a sentence, ask yourself what the author was saying. At the end of a whole paragraph, ask yourself what the point of the whole paragraph was. If you ask yourself questions, you will find that you are paraphrasing the passage in your mind. That will help your understanding. Know where the author stands. Sometimes a passage will contain an evaluation of some ideas of tools or procedures. The author may want to make the point that certain practices or procedures are bad or that certain tools may not be right for a particular job. Be sure you know if the author is accepting or rejecting something.
Circle keywords and phrases. In a reading comprehension test you are not reading for just a vague general understanding of the passage. You usually have to read for detailed understanding. There will be individual words that are important for grasping a point exactly. You do not want to write so much on a passage that it is hard to read a second time if you need to go back to check a detail. But you do want to circle key words or phrases that will enable you to zero in on precise points needed to answer a question.