How do Dispensationalists tell which passages are for Jews and which are for Gentiles?

As I understand it, a key part of dispensationalist theology is a separation between Jews (Israel) and the Church as two separate entities with distinct purposes in God's plan. In discussions with them, I find that they often assert that some passages of the Bible are for Israel while others are for the Church; the process of distinguishing them is sometimes called "rightly dividing the Word of God." However, I often fail to see how they can tell which is which. In a discussion with a dispensationalist pastor I had recently, he seemed to believe that every other paragraph in Galatians is directed at Israel or directed at the Church, and I found myself totally at a loss to be able to follow. I am wondering, **what methodology do Dispensationalists use to determine which passages are directed at which group**?