It is best to read the passages first to get some ideas of what the questions may ask. If you do this, it will become easier to find what the questions are looking for, For this, you don't have to read the passage deeply as just skimming through the contents of the passage will give you enough idea to know where to look for answers. On the other hand, if you are skilled enough to catch the crucial point f the sentence and put it into context, you can look at the questions first and look for the answers.