First off, when you read a passage, understand concepts...do not attempt to memorize details. Let the passage form a picture, movie, or diagram in your mind. Train yourself to do this quickly due to time constraints.
You might also want to familiarize yourself with the different types of writing: expository, persuasive, explanatory, etc.
Before you even look at the questions about the passage, try to answer these questions in your own words:
What is the main point of the article? What is it trying to tell me? What comparisons is it making? What conclusions are the author drawing? What is the evidence for those conclusions? While you are reading the passage, it might help for you to underline some of the sentences that succinctly answer these questions. Remember, your answer to these questions cannot be correct without EVIDENCE from the passage.
THEN, look at the questions and the answers. Sometimes, test-takers will look at the answers without having formed their own opinions of the passage, and the answers themselves will guide the selection...often to a wrong choice.
If you are using the study guide, take a look at the answers you chose vs. the answers the guide has indicated are correct. Look back at the passage and attempt to understand why the other answer is correct. Underline the evidence from the passage that led you to your answer and do the same with evidence for the other answer. Is the difference now clear to you?