The survey is the first step in reading for comprehension. Attempt a quick overview of the reading material. The goal is not to get a complete understanding, but rather to determine what the piece is about. If the passage focuses on the Civil War, is it about "causes of the Civil War," "effects of the Civil War" or "major battles of the Civil War"?
Make the subject of the passage, which you have just determined through the survey, into a question that can be your focus when you read through the passage. For example, if the passage is about the causes of the Civil War, you question should be "What are the causes of the Civil War?" The purpose of creating a specific question is to make you a more active reader, seeking specific answers.
Armed with your question to help you stay focused, you are ready to read the passage. When reading a passage for practice, take brief notes on the passage. When you have finished reading the passage, your notes should clearly state the answer to your question. In the case of the example here, you would have written the cause (or causes) of the Civil War. Be sure to note qualifiers and varied viewpoints. For instance, the passage might note that while historians agree that the Civil War was fought over slavery, many people believe states' rights was a contributing cause as well.
Your vocabulary is another tool for reading comprehension. Obviously a person with a better vocabulary will be better able to comprehend more complex material, so work on your vocabulary every chance you get, well before taking the test. Develop the habit of looking up words you encounter that you don't know.
Being able to read faster is also an asset, because standardized tests are always timed and the SAT time limits are strictly enforced. When reading in anticipation of the test, try to force yourself to read faster without sacrificing comprehension. With continued practice, your speed will increase.