I think having the older sibling be the one who 'introduces' the people to the new baby gives a lot more ownership for him/her. If you can have a few of the adults who will be meeting the baby ask your son if he can introduce them to the baby, that would work. Or, you could just take the initiative and ask him to introduce the baby to (Grandma, mailman, whoever is meeting babe for the first time).
We talked about new babies and what they were like a lot before dd2 was born (dd1 was three). Read books about it, etc.
Once dd2 arrived, we realized that it was really important for her, to have me continue doing bedtime with her (not dh, which is what we'd hoped). And, the first few months, she needed more attention from me, so we ended up having me take a half-hour walk with her every afternoon right after nursing SJ. Otherwise, she would act out and be disruptive.
They get along pretty well now. There are territorial issues and sharing issues which I think in the end are normal for kids and part of figuring out how to get along in the larger world as well.
ETA - also, we had a bag of stickers that I'd wrapped and had handy for when company came and had gifts for the baby but no 'big sibling' gift for Ina. I do think kids keep tabs of that ... if your ds is old enough to be OK with it, fine, but for Ina, as long as she got something too she was OK, even if it was just a package of stickers (which she loved at the time). Now, at 6 and 3, they both understand that sometimes one gets a gift but not the other. But during that upheaval and that young, I thought I'd rather err on that side with dd1.