Personally, I have never experienced sibling jealousy with my own children.
When I was pregnant with my second baby, I told my son who was almost two ,in language that he could understand. We looked at pictures of babies in magazines and borrowed library books etc.
He came with me for some of my midwife appointments and met other children whilst waiting, who were also going to get new baby siblings and he heard the baby’s heartbeat during the examination.
I let Leigh chose the wallpaper for his brothers room.
When the time came and Damon was born, I made a point of not having him in my arms when Leigh walked into the ward to visit. Instead I gave Leigh a big kiss and hug and said meet your brother. When the cover was pulled off Damon there was a present for Leigh (from Damon) I then asked if he would like to kiss his brother. which he did.
When we came home, I tried to include Leigh in Damon’s care as much as possible. When bathing Damon I put the soap out of reach on purpose and asked Leigh if he would pass it to me. “How would I manage without you?” I told him. I also gave Leigh a teddy which I told him to look after and he would mimic the things I was doing with Damon.
When Damon was asleep I tried to spend time with Leigh and when Damon was awake I encouraged the boys to interact. Leigh made a den under the table, so I put the baby chair in there, I sat back watching; Leigh was chatting to his brother.
I did similar things, several years later (but more age appropriate) when my third son was born (I had also gained a step-son by then)
A completely different situation, which I would like to share is while childminding a four year old (the youngest in her family) and a twelve month old baby at the same time, the baby started walking witnessed by the older child. The following day, her mother told me how excited her daughter had been and what a wonderful experience I had given her, as she would not otherwise ever see that, as they were not planning on having any more children.
As always, comments/questions are welcome.