My kids are just over 2 years apart. Here's a couple things that worked well for us I think:
1. have your daughter attend appointments with you. My oldest loved being able to hear the baby
2. Talk about the baby that's coming as soon as you're comfortable with it. If that means today, great, if that means after 12 weeks, great. Once baby's heartbeat is present, miscarriage risk drops dramaticly.
3. let your daughter feel baby "bump". We used that instead of "kick" because we didn't want our oldest kicking back. Worked beautifully!
4. Any changes you want to make (like sleeping arrangement), do it as early as possible.
5. Have people who know your daughter take her for field trips to places that she enjoys. That will help her be more comfortable when/if she's seperated from you.
6. Have someone besides your partner designated to care for your daughter while you're in labor/delivering.
7. We liked the book "I'm a big sister" by Joanna Cole. Both parents are involved in baby's care and the baby doesn't have a gender.
8. Whatever activities your daughter is doing 3 months before your baby is born, keep doing those for 3ish months after the birth too.
9. get out your baby gear (swing, bouncer, etc) a couple months before baby is due so that your daughter can get accustomed to either playing with them appropriately or get used to having this fun looking stuff out but that she can't play with.
10. If your daughter is currently nursing, consider continuing. My oldest nursed through my pregnancy and now my kids have been tandem nursing for over 9 months. If you want more info about this, pm me and I'm happy to share!