How does Golding establish the characters of the two principal boys in the first three chapters of Lord of the Flies, and how does he prepare the...

When all the boys first arrive, they crave some semblance of order, and this is first established by Ralph with the blowing of the conch:

They obeyed the summons of the conch, partly because Ralph blew it, and he was big enough to be a link with the adult world of authority.

The conch, and soon Ralph himself, become symbols for the order the boys need to remain connected to society. As soon as the boys mention electing a chief, Jack says, "I ought to be chief . . . because I'm chapter chorister and head boy." This statement is almost humorous because it is so arbitrary--how does being a good choir member qualify one to be chief of a deserted island? Even the young boys know that it does not, and they quickly elect Ralph, who seems much more level-headed and tells them

"This is our island. It’s a good island. Until the grown-ups come to fetch us we’ll have fun.

"There’s another thing. We can help them to find us. If a ship comes near the island they may not notice us. So we must make smoke on top of the mountain. We must make a fire."

Here, Ralph distinguishes himself as practical and optimistic, and he quickly proves that he also has excellent leadership skills when he gives Jack, who is obviously his competition, an important "job":

"Jack's in charge of the choir. They can be—what do you want them be?"

"Hunters."

This single word uttered by Jack sets up the disparity that soon develops between the two boys: While Ralph focuses on rescue, Jack focuses on the hunt; Ralph on the future, Jack on the present; Ralph on holding onto civilization; Jack on feeding his inner savage. In fact, the first glimpse of Jack prepares the reader for Jack's later behavior:

Within the diamond haze of the beach something dark was fumbling along...Then the creature stepped from the mirage on to clear sand, and they saw that the darkness was not all shadow but mostly clothing.

And finally, once Jack does actually begin to hunt, the reader realizes that he is quickly digressing:

[Jack] tried to convey the compulsion to track down and kill that was swallowing him up.

The two boys who might have even been friends under different circumstances are on vastly diverged paths by the end of Chapter 3.