So you have a baby on the way - and you're worried about how your current kiddo is going to react. Sharing (especially sharing a parent's attention) is tough stuff. I know I don't like when the object of my affection is distracted. 

And - love is not scarce, even if attention sometimes is.

 My oldest is a great big brother - it's a role that he's taken very seriously - and we still had many sad meltdown moments when his sister was a newborn. One example burned on my memory is a time I was breastfeeding and he wanted me to pick him up; I just couldn't do it, and he stood a foot in front of me crying for about 10 minutes. Heartbreaking. On the other side, some of my favorite Mama moments have been as witness to sweet interactions between my kids. No one makes my daughter laugh the way my son does; even if he's the reason she was crying in the first place.

Back to your situation - first, every kid is different, and you are certain to have good moments and bad, and to witness good moments and bad between your children. 

Onto the topic at hand -

7 Tips to Prepare your Kid to be a Big Brother or Big Sister 

Here are some things that I thought made a difference in setting a strong foundation in our kids’ sibling relationship. I must note that my son had excellent daycare teachers while I was pregnant that helped prep him (and us). Many of the suggestions below come from Deb and Rhonda in the Cloud Room (to whom I will be forever grateful).

Use what feels good to you and scrap the rest!

1. Have other grown-ups talk to your child about how cool it is to be an older sibling. Our son's teachers did a "baby unit" so that all his friends got in on the excitement of the upcoming baby. Our daughter was a celebrity in the Cloud Room before she was born. I recommend talking to your older one’s teachers and seeing if they can help you out, even if it's just talking with your child. They might have more specific tips also since they know your kid well!
2. Play pretend with baby dolls - modeling how babies eat, pretend diapering, gentle talking and touching. Our son walked around with a doll attached at the nipple fairly often.
3. Think through ways your big kid can help. Maybe have a diaper station that is at their level (or a stool) so they can hand you diapers and wipes, for example. Or a baby toy station so they can be in charge of bringing the baby something to look at/play with. Or practice their silly faces. There's a reason no one around here gets our daughter to laugh like her big brother does - he's been practicing. 
4. Involve the future big with baby readiness. Our son "helped" put the crib together - less planned and more just what we needed to do that day - and the changes around the house seemed like a good companion to the visual changes in my body.  
5. Reinforce that another baby is more love for everyone. You'll still love your first baby just as much as you do now. And, new babies take a lot of time and it will be hard for them to go from having 100% attention to something much less for awhile. 
6. Think about the "first meet". When our son came to visit in the hospital, we had my husband meet him with the new baby at the elevator. So he met the baby first, and then came into the room and had full access to hug me without his new sister in the way. This somewhat separated the relationship between son/mama and brother/sister. 
7. Plan out "special time" between parents and your big kid. The first couple weeks will probably be on the non-birthing parent, but after mom has recovered a bit it’s good for her to take a short outing with your toddler. If you have family help, special Grandma or Aunt/oldest kid time is awesome. If you’re not keeping your current childcare routine with your older kid(s) while you're on leave, having someone take them out for an hour or two will be important (for them and you).  

Book recommendations (and inspiration lists) for your Big Sister or Big Brother to be:

• I'm a Big Brother by Joanna Cole

• The New Baby by Mercer Mayer

• Poor Carl by Nancy Carlson

• Best Books from Read Brightly

• Another list I like

Quotes from the Front Line

(what actual kids say about being the big brother/big sister): 

• Don’t be mean
• It’s fun to play together
• I help mommy take care of my baby brother 
  
• Theo is my family. Mommy, Daddy, Henry, and baby Theo! 
• Bad.
• I'm 6 now but next year I'll be 7. 
• She's good. I'm good. I love my baby. Can I watch Paw Patrol?