I'm not a big fan of flying, but holidays, client site visits and forming a better working relationships with remote colleagues means that it is likely to keep needing to happen – at least until a Start Trek transporter type device is finally made generally available.
On long haul, they seem typically like to bring around food 30 mins into the flight.... shortly after this switch your watch to destination time… and more importantly switch your thinking and eating to destination time too.
It's often tempting to think about how its 'really' 3am etc... but try not too.
Try to force yourself to the new eating patterns as soon as you can, you probably won't be hungry, but try it anyway. For me this was something I only recently started doing on the back of advise from a US based colleague.
Flying west ie to US from UK, generally feels easier. Resist having a nap on arrival, and do your best to hold out until a reasonable local evening time.
Flying east ie US to UK, I find this a much harder transition. It's pretty key to sleep as much as possible on the flight.... I sometimes deliberately have a bad nights sleep the night before, to increase the odds.
Take earplugs and eye shades.... they don't seem to have these available by default these days (at the back of the plane anyway). Good noise cancelling headphone turn the flight into a much more serene place to be (I have folding Sennheisers). I find the 'meditation' audio channel in the in-flight entertainment is surprisingly effective as getting me to nod off, or at least to making the time seem to pass unnoticed.
Buy water at airport despite the price.... so you can hydrate throughout the flight without being reliant on the stewards.
I load my Tablet (Asus Transformer) with a stack of PDF magazines, and Kindle novels and novellas, but also take a magazine (normally Wired) as you can't use electronic devices for the first and last 15 odd minutes of the flight.