From one to two

Hello, I've been a sahm from a few months before my first baby was born (due to complications). I am now pregnant with my second. Only 9wks so far. I'm wondering how did any of you help your oldest adjust to having a new baby around/ not being the only one? I frequently babysit other children but she seems so much happier once they leave. I'm worried we are going to have issues. She is almost 18months and will be two a few weeks before our second is born. Any tips or tricks? Thank you in advance!