Ralph is the one that learns to blow the conch with Piggy's help and this alone helps to set him apart from everyone else on the island. As the one that signaled a meeting, bringing all the boys together, he gets a head start on the vote that is to come.
The second thing that Ralph has going for him is his stature and his appearance. Golding writes that there was a clear strength about him, that his shoulders and chest are broad enough to suggest that he could become a boxer, that he was tall and strong and beginning to become a man. This too helps to suggest to the other boys that he could be a leader.
And Golding writes that there is another thing about Ralph that sets him apart from perhaps the most obvious choice, Jack. Golding writes: "there was a stillness about Ralph as he sat that marked him out: there was his size, and attractive appearance; and most obscurely, yet most powerfully, there was the conch."
This intangible "stillness" that he has combines with his appearance and the power of the conch to push a majority of the boys to vote for him.
In chapter one there are several reasons why Ralph is elected by the other boys to become chief. First of all, Ralph found the conch which allowed all the other boys to gather and group after the confusion of the crash. By blowing the conch Ralph has already acted as a leader while his competitor Jack has done nothing. In addition to the mystical conch Ralph was also slightly bigger than the other boys and had fair features.