Routine: Both my husband and I have TSA Pre-check, which is worth the appointment and fee, as you can take your kids with you through the express line. This advantage has more than once saved us from missing a flight. The kids line up duckling order and their boarding passes are organized in the same way. The TSA gate agent will typically ask who each kid is and the kid is suppose to answer. We have never needed birth certificates while flying both domestically and internationally, but I understand each country varies on this policy. Once we get through security, the kids use the restroom and fill water bottles to avoid any unexpected delay complications when getting off the ground.
Where to sit: I highly recommend the back of the bus. This is where other families tend to congregate, it's where the white noise is the loudest (muffling infant or grumpy toddler's screams) and the least likely place to get dirty looks. I never feel like I need to buy anyone a drink when I sit at the back of the bus.
Since we typically travel with six to seven people, we usually take two consecutive rows, placing the younger kids behind the older kids to ensure we only kick family members' seats. Please note, you must have an adult per row in case of an emergency for the oxygen mask situation. Also note, you cannot sit in an emergency row. I have found these rules to also hold during international travel.
What to bring: I always carry gum and kleenex on a flight. I also have the kids fill up their water bottles after passing through security to stay hydrated and avoid travel headaches. We like our kids to share iPads after they exhaust reading material, so we also carry a splitter so two pairs of headphones can attach to each iPad.
When to fly: We like to fly early morning flights. I have never had a pleasant flight with a baby a night.