Everything that everyone has posted is spot on. So read them through once or twice.
Here's my .02 worth as I'm based there to help get a sense of what it takes to get off the gate and on your way: But before that---we all make mistakes online. First off, don't be afraid to fess up either to the other guy or ATC...Its how we learn and keeps from making what may be a minutiae situation anything worse.
ORD will spit out a taxi clearance with the best of the auctioneers. So I always write this stuff down--every time. I can't tell you how many times taxiways or runway clearances got changed (5 runway changes are my best to date). Therefore when your trying to run checklists and new performance numbers, your not trying to remember what the last change was and how to get there.
Push-backs:For the AA ramp (131.87-if that's what you will be using) I like to put it in COM 2. That way when they switch you to metering (on COM 1---121.67, then ground 121.75)--its just a push of a button. Many times early in the morning when there is little traffic, these guys are spitting out your taxi clearance by the time your flipping the switch--IMO
Make sure "if" your aircraft has the ability, put the altitude rings in your Nav display--you need to be at 3000' by 5 miles and 4000' by 8 miles. Also, and this is a nice "gotcha" if your not paying attention---you need to maintain 250 kts until otherwise directed.
Congrats and welcome to the line.............................................. ..........