How does Ralph assert his chieftainship, and how is this effective?
The first thing Ralph does upon becoming chief is to grant shared power to Jack. Ralph is perceptive enough to notice Jack's mortification at being voted down, so he is "eager to offer something." He concedes that the choir still belongs to Jack and lets Jack choose what they are to be. Ralph is being nice here, but the decision comes back to haunt him when Jack's role as hunter becomes most valued by the boys.
The next thing he does is choose two to help him explore. He selects Jack and Simon while he spurns Piggy. He then delegates the cataloging of the boys to Piggy.
After the exploration he gives a pep talk to the boys about rescue that is well received, but at the mention of building a signal fire, he loses control of the boys, resulting in the first deadly fire on the mountain. Thereafter Ralph shows himself to be a participatory leader; he pitches in building huts. However, once again he is unable to control the boys, and most of them run off to play, leaving only Ralph and Simon to continue struggling with the shelters.
Ralph's most effective display of leadership is when he learns the signal fire has gone out when the boys kill their first pig. He reprimands Jack, defends Piggy, and requires the boys to re-light the fire while he stands still and silent, observing their efforts. Although he attains his immediate goal of having the fire lit, and a secondary goal of exerting his authority, this display widens the rift between him and Jack, setting up their ultimate conflict. After that Ralph is able to retain some loyalty by reminding the boys about rescue, but before long, he has lost all his followers except Piggy and Samneric.
Although Ralph displays a compassionate heart and has good motives, wielding his chieftainship based on kindness, participation, and long-term goals turns out not to be very effective with the large majority of the boys.
Ralph sees his authority being tied to making rules and keeping things in order. He is very pleased with the suggestion that the conch is a symbol of order. Ralph appreciates that the conch needs to be held in order for everyone to listen. Ralph is bent on making sure that the boys build shelters and maintain a fire and do things in an orderly in order to be to be rescued. He was elected, after all, and this means that he gets to be in charge.
The problem is, Ralph tries to assert this power by reasoning with the boys and pointing out the issues and appealing to their sense of reason and logic. It works for a time as long as the boys still remember civilization, the idea of rescue and the hope of return to civilization.
But as Jack, his hunters and the savage lawlessness of his authority takes control, Ralph's method of asserting his power and control begins to lose its effectiveness. The boys get tired of meetings and complain about talking too much. In the end, the conch is destroyed at Piggy's death and Ralph's authority is gone for good.