My daughter is 5 and going to be a big sister in November. Really it is about forming independence during non-essential times (like play time). Forming respect for personal time during the day will give you time with the baby. So we've begun encouraging her to do things for herself like getting ready for bed (brushing teeth, going to the bathroom, picking up toys, etc) then she is rewarded with time together reading, praying, etc. Also I homeschool so it has been essential for her to understand that school time is broken up by free-time (which will later be time for me to feed baby or baby nap time). That free-time has activities whether quiet ones like playing outside or coloring, or turn on the music and dance or watch a TV show. If your kid will be going to or is in Kindergarten then you will simply need to make before and after school focused on her.
The other thing is "helper" mentality. Don't expect her to help, but encourage her to help through praise. So right now I have trouble picking things up off the floor, and if I am carrying laundry and something falls I usually ask her if she would help me by picking it up. Same with clearing the table or letting the dog out, etc. She has the right to say "no" in a polite way, but most of the time she is more than willing to help. When little baby comes along having that training means I can ask her to help retrieve a blanket or bring me the phone etc when I am nursing or otherwise have my hands full.
Also just make that one-on-one time your full attention time. A second child is just that another demand on your attention. It is okay to let a baby cry a few minutes while you finish reading a story, but it is also okay to expect your daughter to wait until you've finished feeding the baby. That one-on-one time should be equally treated meeting their needs for attention. If you don't cut short or allow interruptions (save emergencies), to interfere with your one-on-one time then your daughter will learn to respect that baby has time now and I'll have time later.
Hope this advice helps you. I know it has brought me much peace of mind to watch my daughter grow in her own abilities and to respect my private time which will soon be consumed by another child who will grow and learn the same.