We've been to New Zealand (when DS was 6 months - 36 hours door-to-door!) and New York (he was 13 months) and both times it was nowhere near as bad as we expected. (DS is a pretty easygoing baby and isn't walking yet, which helped).
You should definitely try to get the bulkhead seats; you get extra leg room and DS was happy to crawl about on the floor under our feet for a surprisingly long time. Don't bother taking too many toys, DS was happiest pulling the magazines out of the seat rack, emptying stuff out of my bag and generally creating a mess. Drag mealtimes out as long as you possibly can to waste time and let DD crawl or walk around to burn off some energy whenever you get the chance .If DD cries, don't worry what anyone else might be thinking - most people are sympathetic, and if they don't like it they can put their headphones on! If you're in the bulkhead seats you may be surrounded by other parents and babies anyway.
With regard to jetlag, there's not much you can do to prepare, but I think babies are pretty flexible. New York is 5 hours behind but we flew during the day and by the time we put DS to bed on the first night it was about 7pm (his usual bedtime) and he was so tired he slept right through. When we got home he got straight back into his old routine.
NZ was a bit harder and took a few days for us all to adjust. But I think DS coped better than I did, to be honest. We found it really helpful to stick rigidly to our usual evening routine of bath, feed and bed, so that even if we were staying in unfamiliar surroundings our routine stayed the same.
The only other thing we've found is that DS tends to get a bit of a cold after he's been on a plane, but nothing serious.
If all else fails, legophobe is right - however much the journey seems to drag, it won't last forever! I hope this helps, have a lovely holiday xx