In my opinion, Golding teaches one major lesson about the abuse of power.
Power must be given to people who will use it appropriately. I think in the beginning of the novel, we can all agree that Piggy would have done the right thing and applied intellectual strength to every decision and need, but Piggy didn't have star power with the boys. Ralph worked as best he could to lead appropriately, but when the boys begin to follow Jack, we see the most destruction. People who use power for their own gain end up doing the most damage to everyone else.
Another related issue is that power issued due to a vote can easily be later lost. People want to respect their leaders. However, Ralph failed to produce and manage the boys to the point that they could see the benefits of his leadership. This is why many were willing to go off with Jack when Jack presented an attractive alternative.
Without power one cannot abuse. This is an obvious lesson brought forth in William Golding's Lord of the Flies. In this story, both of the leaders, Jack and Ralph, are able to abuse other boys on the island. Jack is able to abuse all of the choir boys because of the power Ralph gives him. At the same time, Ralph is able to abuse the boys, mainly his constant mistreatment of Piggy, throughout the book. However, Golding shows over and over again that power is most often taken to the extreme. Jack uses his power to create savages on the island, leading to the death of two innocent boys. Power, in the wrong hands, can only be abusive. Golding teaches that power must be placed in the right hands, and there must be a checks and balances to prevent abuse. Piggy was the balance for Raph, unfortanately, Jack did not have anyone to balance his power. Power was all he wanted, and because of that, the island became a place of evil.