My daughter, Angel, was about 6 1/2 when we decided to TTC our second, so I was in your position about a yearl and a half ago. She had been wanting a sibling for quite some time though. The entire way through my pregnancy we called the baby "OUR baby" with her, and I bought a book (Baby Oh Baby The Places You'll Go - A Book To Be Read In Utero) that she read to the baby a lot. We also took a special trip to Build A Bear Workshop where she made the baby a bear that she brough to the hospital. And at the hospital, I gave her a present as well - fabric markers and a pack of t-shirts and a pack of onesies so she could make shirts for herself and her new little sister. I think that keeping her involved with everything, and giving her things to do to get ready for the baby really helped. She is the best big sister! She loves helping out with Alana and is really great with her.
Hope this helps a little

Good luck TTC! I hope you get a BFP soon!!