I did my DC1's first ever flight at 15 months. Roughly same flight length.
What do I wish I'd known? That this is the worst possible age for flying! Big enough to want to move around but too young to understand why they can't. Too young for own seat. Non-verbal so hard to reason with.
However I was alone, and unprepared for how awful it would be. And we got delayed on the plane before departure with seatbelt light on for 45 min. Yes that's 45min of screaming trying to keep toddler in the infant belt. I actually cried.
There are loads of things I wish I'd known and I'm sure it won't be so bad for you. So here's what I've learned many flights later...
Are you alone or with DP? That will make a huge difference. Space wise and also having someone to pass stuff. If you are alone - do not drink any fluids yourself in departures.. It's only 2 hours, you don't want to be using the loo if you don't have to.
iPad with fave shows. Lots of new poundshop toys that can appear at regular intervals. Fave snacks and treats. Plenty milk and water (buy in departures and decant you don't want to be waiting on the trolley) to sip when taking off/landing.
Time the final nappy change for just before boarding. I have only had to change nappies on a couple out of many flights. Put on lots of barrier cream as you can't change them when seatbelt light on.
Make sure the toys aren't too small as you will be constantly trying to get them from down side of seat.
If you can prebook seats book the back row so you don't feel the eyes of 100 passengers on you (while struggling with a screaming, writhing toddler in my case) . Also the baby change is usually back there (flips down over the toilet) .
Take a sling as sometimes the buggy doesn't come back at the gate and you end up with a long walk to luggage reclaim. Also good to switch to this in queue at gate for boarding.
If hand luggage only, take a wheely case and a rucksack with lots of pockets/sections as changing bag (infants usually get this as their allowance) . Make sure you have all the things for flight in easy to find places as this goes at your feet.
Always get buggy tagged and take to gate. Even if toddler doesn't sit in it on departures it gives you somewhere to put all your stuff while running around after them. Don't let them sleep in it then. Remember most airports will make you fold it and put through scanners at security.
Exercise them in departures. Running up and down quiet long hallways is good and a lot of airports are starting to have little soft plays - google location of it so you don't miss it.
Bit small for colouring books but small sticker book might be good (don't get A4 they are awkward on tray tables).
I have since flown loads with one or two kids and it has been fine! Babies are so easy, esp if breastfeeding and older kids love tje experience and can be distracted and bribed much more easily.
Good luck. At least it's not long haul