My oldest son will be 18-19 months when my second son will be born.
My daughter was 2 when my son was born. Was worried she would be jealous. Their was no jealousy at all. The thing to remember is for first few weeks all your new baby needs is feeding, sleep and to be kept comfortable. I would always refers to the new baby as our baby. I did not let people come in and make a fuss of the new baby. I made it clear to family and friends if buying gifts to buy for my toddler rather then the baby. I would have her sitting beside me while I was feeding the baby and I would chat to her or watch one of her favourite programmes while attending to baby. It's the simple things. I had plenty of time to bond with my baby on night feeds. And by the time my baby needed more attention and more interaction she was use to having him around and they have a great bond now.
My son will be 2 in July and i am due June 24. I have been preparing him I talk about his baby sister he knows she's in my belly I tell him she'll be here soon . I have also started him helping me more which is easy since he is getting independent so that way he doesn't feel left out and he can help with the baby. I don't know from experience yet but that's just the steps I've taken to hopefully prevent a lot of jealousy.
I'm currently 32 weeks with my third child in 4 yrs. My two older children are 1 yr and 2 weeks apart and when this one arrives my kids will be a few months shy of 2 and 3 so trust me when I say I get you! Right now we've been practicing with a baby doll that my daughter has - kisses, letting me have time with the baby, etc. I have the kids bring me diapers, wipes, pick out the outfit for the day, etc as well - make being the big brother fun and tell him how proud/thankful you are when he does things. The biggest thing is making sure you get 1-1 time with your older one. When your newborn is napping make sure he knows that is his time with you, let him choose an activity to do - puzzle, book, coloring, etc. Also having something new when the baby arrives is good too. My oldest will be getting a new doll to care for and my younger one will most likely be getting a new book. If your on Pinterest there are a lot of "sibling kit" ideas.