First long-ish flight. Looking for advice!

Apologies if this is rather unnecessary as my flight isn’t that long compared to what a lot of you have done, but on May 1st I’m flying to Madrid from Toronto which is around 7 1/2 hours? This will be my first time leaving North America and the farthest flight I’ve done is about 5hrs to Los Angeles, which, as a 6”4 guy was quite uncomfortable. The flight will be an overnight one but I’ve heard it’s a bad idea to sleep on these?

I’m looking for any advice on things like which seat I should try and snag, what things I should bring on the plane with me to stay occupied etc. again, I’m sure some of you will laugh at the flight time but I’m still sorta dreading it