Note: Page numbers vary among editions, so I will include the chapter numbers for reference.
In the first chapter, Jack is noted to be the "most obvious leader," yet Ralph is elected to this position for a variety of reasons. He isn't the natural leader that Jack is and has...
to consciously work toward maintaining a leadership position, which becomes an increasing struggle as the plot progresses.
In the first chapter, Ralph acknowledges that the boys both want to have fun and be rescued. He calms their fears by telling them that his father is in the navy, and he knows that there aren't any undiscovered islands left. Although the reader knows that this can't be true—the ocean is incredibly vast, after all—the idea that the Queen knows where this island is and will send a ship to rescue them calms the boys. In a real stroke of leadership, Ralph tells the group that in order to be rescued, they need a signal fire on top of the mountain.
In chapter 3, Ralph confronts Jack about the way he pulls his hunters away from the task of building shelters. Ralph reminds him that early on, everyone committed to working hard on construction until that task was finished. On this day, he and Simon were the only ones left working on shelters while the others play and hunt. Since Jack hasn't produced any meat for his efforts at this point, Ralph questions his abilities and use of time. This infuriates Jack, but proves that Ralph isn't afraid of a confrontation to address critical issues for the group.
In chapter 4, Ralph shows that he understands the priorities of survival better than Jack does. Jack's group allows the signal fire to go out just as a ship appears on the horizon. While Jack defends the group's need for meat taking top priority, Ralph realizes that surviving on the island isn't the primary goal—getting off the island should be the focus.
Ralph and Jack continue to engage in conflict as the plot intensifies, and Ralph proves incapable of harnessing Jack's energy. While Ralph isn't a strong leader and does struggle with getting the group to follow his direction, he has moments where his leadership abilities shine.