For those who have second kids, how and when did you start preparing your elder kid for the new baby's arrival?

My kids are only a year apart, so it was not easy explaining another addition to a child who was below a year old. My hubby and I showed him books of a family with 2 children, showed him scans and were not quite sure if he even understood what was going on. But as soon and baby #2 came along, he got it. And he started accepting it pretty well, probably because he had a buddy to play with (read: fight with) every single day!