Realize that a lot of things might not go the way you expected or wanted them to. There are a lot of unknown variables in pregnancy, childbirth, breastfeeding, and raising kids in general.
Plan financially. Figure out how much it will cost to add a child to health insurance, figure out how much formula will cost should you need or want it, add up the cost of diapers per month, decide whether you’ll want to move to a larger apartment or home and figure out how much that will be, add in costs for increased utilities, plan for whatever furniture items you’ll want, and then add in some more in case you need to unexpectedly buy things like a humidifier or prescription cream.
If you’re the kind of person (like me) who has to plan everything and be organized all the time, try to prepare yourself for the reality that a lot of the time you are going to just be in survival mode and have to let some things go. Those first few months after the baby is born, when someone gets sick, if you go back to work, if your husband is traveling for work, when the baby is teething, whatever…there will be a lot of times when laundry piles up and you have cereal for dinner, and the floors don’t get cleaned, and so on. You focus on keeping yourselves alive until you have a little more energy or time.