This is a tough question to answer considering diction is in part defined as the sound and pattern of speech, but we can also focus on word choice.
1. I like Golding's paragraph prior to the trip to Castle Rock. "The green light was gentle about them and teh conch lay at Ralph's feet, fragile and white. A single drop of water that had excaped Piggy's finders now flased on the delicate curve like a star." Our attention is drawn to how easily broken the power of the conch can be.
2. Just before Roger drops the boulder on Piggy, Golding gives us some excellent atmosphere. "The storm of sound beat at them, an incantation of hatred. High overhead, Roger, with a sense of delirious abandonment, leaned all his weight on the lever." This slow build up to the death of Piggy provides us with a ton of background noise in our own heads.
3. After Piggy is struck, a very simple sentence shows us how quickly the power on the island has switched into the savages hands. "...the conch exploded into a thousand white fragments and ceased to exist."
4. Finally, before Ralph finds himself completely hunted, he contemplates his precarious situation. "He knelt among the shadows and felt his isolation bitterly. They were savages it was true; but they were human, and the ambushing fears of the deep night wer coming on."
There are more examples in the novel because of Golding's wordiness, but these will help you out.