The first rule that Ralph establishes is introduced in chapter 2, "Fire on the Mountain." Ralph creates the rule that only a person who is holding the conch shell may speak; everyone else must listen.
And another thing. We can't have everybody talking at once. We'll have to have 'Hands up' like at school . . . I'll give the conch to the next person to speak. He can hold it when he's speaking.
This rule ensures that anyone who wishes to speak will be heard. The conch shell symbolizes law, order, and civility. Later in the text, when the conch shell is broken, this symbolizes the loss of law, order, and civility.
Other rules that Ralph establishes in the novel are that water should be stored in coconut shells underneath the leaves, that rocks (instead of the area near the fruit trees) should be used for the restroom, and that a boy must always be watching the signal fire on the mountain to make sure that it never goes out.