I have not flown much since 911 (once). But I've flown a
lot.
I don't know if this still works (regarding getting seats), but I always showed up extra early (and sober and perfectly fit) and did not do curbside check in, went through the line in the terminal, and requested an exit row (claiming my Air force background ensured I would help people get off the plane in any emergency) (and yes, I know I cannot order alcohol in an exit row seat).
Exit rows always have the most leg room in coach. They may not have the best view from the window (I always take isle), and they may be noisy over/near the engines. I dont' care, I just want more room.
Even if you can confirm seats online, I don't think they ever confirm exit row seats, except at the airport where they can visually check you out in person as (physically/mentally) qualified to man the emergency exits.
PS, I had a lot of rough rides, but never actually had to get off a plane via the emergency exits.
Another thing is to carry
both ear plugs and shooting muffs. Wearing both together helps you not hear all the screaming babies and children, and lets you sleep. Depending on luck, these plugs and muffs can come in handy at motels too.
Standing up and offering to buy red wine for everyone on board age 2 or under doesn't work, and makes some people boo you (but others enthusiastically cheer you).

It's really something when sitting in the toilet (even with the smells) is a better seat than any seat in coach (except maybe the exit rows). But if you stay in the toilet too long, they start banging on the door asking what you are doing in there.
BTW, jet lag is far worse going over than coming back. All overseas to Europe flights leave in late afternoon, and if you try to get as much sleep as possible, you will minimize jet lag. Otherwise, your first two days over there are like walking around hung over.