If you get smashed at the beginning of the flight you'll be hungover by the end. I'd drink during the layover but not before! Hopefully then you can nap on the second segment. Definitely drink loads of water. I'd get a bulkhead window so I can lean on it but also go to the restroom.

Sound isolating headphones are essential. I don't like ANC so I use the Sennheiser CX 300 IIs, which have great sound quality and are cheap enough that losing them is ok. But you can also try Airpods Pro or Boses. Also don't forget to have enough offline music available!

Also make plans for food