Regardless of whether your story is told in first or third person point of view, the reader should be able to see the world of the story through the eyes of the protagonist.  The reader should also be able to hear, taste, smell and feel what the protagonist is experiencing at any given time.  By allowing the reader to get inside of the head of the protagonist, the reader can identify and sympathized with him.   The reader can grow an attachment to the protagonist and care about what happens to him.  The reader will be invested in the story and want to keep turning the page.  In order for the reader to experience the world through the eyes of the protagonist, the writer must be able to convey this experience.  I often put myself in the shoes of my protagonist in order to get inside of his head and really understand what he is feeling.  In order to do this, I need to have a thorough understanding of his back story.  What was his most traumatizing experience?  His most joyful experience?  His biggest regret?  What is his greatest challenge, and what comes easily?  What is his favorite food?  Color?  Type of music?