I posted this a little while ago before I saw your thread to help someone:
Ralph: Represents the good qualities of leadership. For example, Ralph is caring and considerate. A quote which you could learn to support this would be 'You couldn't get a beastie, a snake thing, on an island this size,' explained Ralph kindly'. Here, Ralph is showing that he has good leadership qualities in terms of being able to look others and keep them confident.
Ralph can also be firm. This is shown when Piggy expresses his thoughts about Ralph telling everyone his nickname. Ralph replies to Piggy - 'Better Piggy than Fatty... with directness of genuine leadership'. This shows that Ralph has a strong and confident personality, and makes it clear that he is charge - which is essential in a good leader.
Ralph also represents that the strongest of leaders struggle at points. Clearly, Golding was thinking of Churchill in WW2 (it is essential that you understand that the novel was based on WW2 for your exam). For example, 'I ought to give up being chief'. However, Ralph does not give up, due to the influence of Piggy, and consequently this shows brilliant leadership.
Ralph does also represent civilisation. Ralph wants to turn their natural tropical island into a civilised society. For example, 'We need shelters'. Not only does he genuinely need them, but it is quite clear that he wants them as well, in comparison to Jack who wants savagery. Ralph does also want to stay civilised in terms of cleansiness. For example, 'Maybe we ought to go back to how we used to, you know, washed and hair brushed. After all, getting rescued isn't a game.'
Jack - Jack does represent dictatorship. This is displayed via the way that he is demanding and doesn't value other people's views. For example, when he gets the boys to tie up Samneric, he says to Ralph 'See? They do what I want!' Clearly, this is an example of a dictator. More examples include the way that he doesn't appreciate democracy, 'We don't need the conch anymore', '******** to the rules'.
He also represents savagery. This is displayed via his obsession with hunting. 'All you can think about is pig, pig, pig (from Ralph), 'You're all a bunch of bloody savages (from Piggy). Jack doesn't care about shelters, nor being rescued to civilisation - his excitement from his hunting overuled his 'supposed' disapointment from not getting rescued earlier in the novel.
Furthermore, Jack does actually lose the name 'Jack' and becomes 'the Chief'. Some people have interpretated this as Jack losing his name symbolising Jack losing all of his civilisation.
Finally, Jack does represent evil, in contrast to a character like Simon who represents goodness. For instance, Jack is the first character to do anything violent - he thumped Piggy. 'His voice was violent', is a quote to support this. Initially, as well, Golding instantly describes him with an evil image - 'Staring out of his face were two blue eyes, frustrated and turning, turning to anger'.
Simon - Simon represents a Christ figure. For example, Simon talks to the Lord of the Flies. The name of the book (The Lord of The Flies), does translate to 'Beelzebub'. In the times of Jesus, Beelzebub was a name for the devil. In the Bible, it says that Jesus was tempted by the devil, similarly, Simon was tempted by the Lord of the Flies/Beelzebub. Simon is also sacrificed in their ritualistic dance, similar to how Jesus was sacrificed for our sins. Simon also comes down the mountain, like Jesus did in the Bible.
Piggy - Piggy does represent democracy. It is Piggy who informs Ralph about the conch, with it's purpose and how to use it. Piggy does regularly remind Ralph that he was elected chief ---> he is supportive of democracy. Democracy is also shown through Piggy when he is at their meetings - 'I've got the conch! I've got the conch!' Clearly, he is saying that this is a democratic society, let me speak.
Furthermore, when Piggy dies, it is the end of democracy, because the conch which symbolises democracy dies with him. 'The conch smashed into a thousand fragments and ceased to exist'.
Piggy also represents discrimination. For example, in the war, there were Jews and other groups who were discriminated against, because they were different. It is Piggy who is the most unusual on the island, and it is him they pick on - 'Piggy' 'Fatty' etc... An example of discrimination is shown at their first feast, when everyone but him is given meat. It is Simon, the Christ figure who gives him some.
Piggy does represent civilisation, through his glasses. His glasses are a symbol of civilisation - they are artificial, and furthermore powerful. Golding shows us that civilisation suffered during the war through the damage of the spectacles. For instance, when the first lense broke, civilisation was damaged. By the time they were completely destroyed, so was civilisation.
Piggy is also a representation of those who assisted our leaders. For example, every great leader, whether it is Churchill or Obama, they have people advising them. Piggy does this regularly with Ralph - because he is intelligent and organised. An example would be how he wanted to have a register (which is also another example of civilisation).
Roger - Roger does represent those people in our society who pure evil. For example, Jack initially hesitated killing a Pig, but Roger on the other hand, he went to kill it straight away. Similarly, it is Roger who killed Piggy.
When Roger went to throw stones at Henry, he threw them around Henry, because 'his arm was restrained by civilisation'. When civilisation is gone, his acts become more evil, such as murder. Roger does represent those who are not bold characters, who are evil with secrecy.