Where in the book is Ralph shown being a good leader?

Because page numbers can vary according to the edition of Lord of the Flies a person is reading, here is an answer with chapter references.
In chapter one, "The Sound of the Shell," Ralph demonstrates that he can be diplomatic and inclusive when the boys vote to have him become the chief. Ralph recognizes that Jack feels rejected, so he quickly offers to appoint Jack to leadership over the choir, who will become the hunters.
In chapter two, "Fire on the Mountain," Ralph establishes some ground rules, beginning with the role of the conch in meetings. The person who holds the conch will be empowered to speak, and the others must quietly listen. The rule enables an organized method of communicating information and opening dialogues. In the same chapter, Ralph is able to raise morale by telling the boys that the island is mapped and that there will eventually be a ship passing that will rescue them. The narrator says that when the others heard Ralph's assurance, "they liked and now respected him."