One reasonable approach to the novel is to regard it as a political work. Golding sugests that reasonable, benelovent, "fair" governments are ineffectual compared to the compelling dynamism of an auturocracy. In order to repel such dictatorships, democracies need to be willing to dispense with some of the liberties which their people so cherish. Jack's tyranny is fearful, but it's fun. It's exciting. It brings out the beast in the boys, just as a charasmatic dictator brings out the beast in society.
Take a look at any situation where supervision is removed and see how people of any age act. In a school setting, do the students act the same when a teacher is out of the classroom as opposed to in it? Do teachers act the same when a principal is supervising? It's the same for most jobs - do any employees do the same things when they know a boss is watching as opposed to when they know a boss isn't?
This novel is a large, vicious view of that concept. What happens to people when authority and accountability are removed? Golding contends that we're savages underneath and can't help but revert back to savage behavior. However, there is always the Ralph or Piggy who is able to retain those civilized ways. Unfortunately, they're a minority with a large uphill battle to fight.
Lord of the Flies represents what goes on in our society in several ways. First and most simply, the boys on the island have been trained and educated well. They should be able to live moral lives, and to organize a peaceful and healthy society. That they cannot points out some of the weaknesses in our civilization.
Second, individual characters represent different types of person from our society, and therefore can be read as commentary upon them.
Third, and most generally, they form a society in miniature. Therefore, what happens in their society mirrors what happens in ours (and vice versa).