T.R.
Well, my oldest was still little when I became pregnant with my youngest but I think what we did would still work with older children.
We made him part of everything. When I had ultrasound appointments he went, the first time they were able to hear the heartbeat, he was right there. We also let him pick out stuff like sleepers, onesies, just basically all the stuff that you buy before the baby is born.
When his little brother was born, he was at the hospital and was allowed to hold his baby (that's what he always called him..."my baby.")
When we brought the baby home, when the baby needed changing, we asked him if he would mind going into the baby's room and getting a diaper and the wipes, or when the baby was in the bassinet and spit his paci out and started fussing, he would go over and put the paci back in his mouth, he would wind up the baby swing when it stopped, just simple stuff like that to make him part of it...like he was actually helping to take care of "his baby."
He never showed any jealousy towards his baby brother. They are a lot older now and sure, they fuss since that's what siblings do, but they are also very close.