This isn't going to be a terribly helpful post (I like to set expectations up front!). It's the same thing you hear time and time again, "You know what's best for your kid." The same stands for getting your child ready for a sibling.
My second child (of unknown gender) was going to be born about 2 years, 8 months after my first boy. My oldest is very easy going...isn't one for tantrums and after years in daycare, was generally well adjusted around loud babies and people in general. I was a lazy pregnant woman. So I did virtually nothing. We talked about a baby in my giant belly, but we couldn't discuss the gender (because we didn't know) or the name (because we didn't have one...see, I told you I was lazy). I got some books from the library, but they didn't have cars in them so he was not interested.
We transitioned daycares a few months before the due date, which is apparently a bad thing. And we moved his bedroom the day of the birth. Another big no-no. However, I did let him keep his pacifier and hadn't attempted to potty train, but those were battles I was not willing to fight at 9 months pregnant. Yet, the transition went off without a hitch.
We connected moving to a "big boy" room with becoming a big brother. The baby and big brother exchanged presents at the hospital. Everyone does it, and it seems to work. However, I think the kitchen in the post-partum ward, stocked with apple juice and graham crackers, was a bigger hit. After my oldest came to visit for the first time, he cried because we couldn't bring the baby home that very moment.
I tried to spend a few hours with my oldest every day. I took over bedtime duty for him and made sure I gave him lost of attention once my husband came home to take over baby duty. We had lots of playdates with other new moms. The moms sat with the babies and bigger boys played amongst each other, not feeling the least bit deprived. Even if you don't need help the second time around, take it so you can spend some extra time with the oldest.
I know there is no groundbreaking advice here. Just take it day by day and do what works for your new family. Easy going kids will have an easy transition. Older kids seem to have an easier transition. But kids will surprise you. I think they're just plotting ways to torture their little siblings in the future.