Ralph is a good leader because of his physical prowess, his confidence and readiness to act that this produces, and his ease with people. He's also good in part because he doesn't get caught up with theory or questions the way Piggy does, and is not, at the start of the book, subject to fears or anxieties.
The author shows this in two ways: through showing him in action demonstrating these qualities, and through showing how others (such as Piggy) react to him.
The qualities that makes Ralph a good leader is his maturity and leadership skills.
The writer, William Golding, doesn't straight out mention the good qualities of Ralph, but the author creates Ralph's personality by his actions.
For example, whenever the other boys were laughing and snickering at Piggy. Ralph stood still and didn't laugh with them, which shows his maturity.
Another example is that he always lead the group and made sure the fire kept on going because he knew that that was the most important for saving everyone.
in addition to what i wrote before, i forgot to add this, the only reason Ralph is elected cheif is because he has blew the conch he is no more qualified to be cheif then Jack, Piggy, Simon, or Rodger for that matter
he is more or less like a politician he wants to make everyone happy he goes with the crowd contrary to what evry one else says he isnt a natural born leader so dont get that mixed up