Girly girls should be pleasant, sweet, modest, and constantly in a good mood. Just like a Disney princess!
Always try to have a smile on your face, and be helpful and willing to do someone else a favor. You want to set a good example for your peers and be a leader, someone other girls look up to.
Remember to be nice to everyone, not just your friends or the people that are in your group. Everyone deserves a chance. Don't exclude people from games, gifts, etc. Keep your promises and don't gossip.