There is a book called "I'm a Big Sister" by Joanna Cole that is very positive and talks about how the baby will be small and require attention. When I was looking at books, a lot of them have a jealousy aspect, which I did not like. My son hasn't been negative towards the "baby in Mommy's tummy", so I did not want to plant any jealousy ideas into his head. I got the "I'm a Big Brother" book, written by the same author. Mercy Mayer also wrote a good book "The New Baby". My son didn't like it so much, but it is also a positive book.
The hospital I will deliver at has an online "maternity ward tour" video. I've watched it a couple of times with my son (he's 2 years 8 mos) to explain to him "This is where Mommy will be when Julia comes." It was a really short video...about 8 minutes. They don't show anything graphic, just a couple checking in, the L&D room, the nursery, etc. I don't think he fully understands the details, but he now has this idea that Mommy will be gone for a little while, but he can visit his sister and then we'll be home.
As for sharing the love, we started to plant seeds. When our son says he loves his trucks, we ask "Do you think Julia would love trucks too? Would it be nice to share with her?" We try to keep the new baby in conversation when it seems appropriate, and we always try to focus our words on making him in control of helping or sharing.
I hope this helps. I'm due any day now, so I don't know if any of these methods will bear fruit. But that's what we've been doing.