From just the first chapter we know the following things:
Ralph wants to be a leader and is interested in maintaining some kind of order among the boys. He wants to go along with Piggy's proposals to have the boys vote on things, to use the conch as a symbol of who has the right to speak, etc.
We know that Piggy is fat and wears glasses and that he has been made fun of for as long as he can remember. He is not comfortable putting his ideas forward on his own but feels comfortable working through Ralph or someone else.
We know that Jack wants to be a leader but doesn't have the confidence of the boys yet. He also wants to hunt but really doesn't know how to do it yet.
We know that Simon is important even though it isn't quite clear yet but having been chosen for the exploration we know that he will become integral to the story.
We just know the twins are really friendly and relatively mature.