What rule does Ralph establish?

Ralph establishes the rule that whoever is holding the conch has the right to speak. Only he, as chief, can interrupt them.

The conch was not the only rule made by Ralph. In this 'scene' in the book, all the boys are gathered and the conch thing is agreed. But in so doing, a sort of democratic authority get put on the conch itself instead of Ralph. But still Ralph, as the leader, can still interrupt whenever he feels it to be necessary.