Something you discover when you start to fly somewhat often is that your body is damn stubborn. You would think that after not sleeping too well in a noisy plane for 10+ hours your body would be very glad to crash on a quiet room on a comfy bed, but that's not the case.
You'll wake up at stupid o'clock, rub your eyes and sigh as you look at the time and realise not even the birds are singing yet, because it's just 2 AM. But your body says "nope, it's 10 AM, wake up, you lazy person!"
I spoke to some people in the office and they told me they would be interested in learning about my 'tricks', so I decided to post them here. But please note that this is just my method. It might not work for you. Who knows, it might even be dangerous if you have certain medical conditions.
Pretend you're in the new timezone as soon as you jump on the plane
E.g. if I board a plane from London to San Francisco at 18h, it's 10 AM there. The flight takes about 11 hours, so by the time I land it will be 21h in SFO, but 5 AM in London, and I'll have a severe urge to sleep during the flight. Don't! Try to stay awake as much as you can. That way, when you finally get to a proper bed, you'll be really tired, and you start convincing your body to "shift timezones" a little earlier.
Drink LOTS of water
That unpleasant sensation you start feeling halfway during the flight is not only sleepiness, it's also dehydration because the cabin air is way drier and less dense in oxygen. You might be tempted to accept one of the juices, fizzy or alcoholic drinks they'll offer you, but seriously, just opt for water---you don't need those extra calories.
I've heard you should drink 1 litre of water per timezone. That makes 8 litres in my usual case, which would be brutal to drink in a day, so I space it out during the days before and after flying. I also advise buying one of those 750ml bottles of water in the airport (or bring your refillable bottle with you!) and drinking it throughout the flight, because whatever they offer you will not be enough. Yes, you'll have to go to the toilet more often. That's why I sometimes choose aisle seat, even if I don't get "views" (but if you fly by night there are hardly any views, anyway).
Don't eat crap, and don't eat too much either
Your body not only wants to sleep at its usual hours, it also wants the food at its usual hours. But you'll be eating at totally absurd times and disrupting its usual cycle, so your stomach is going to be upset at you. VERY. UPSET. So go easy on the food and drinks, and on the amounts. It's OK to try new things, but don't overdo it, because then you'll be unable to sleep... for reasons other than insomnia.
I deviate from my "pretend you're in the new timezone" rule here, and usually have some sort of "healthy food" with me to eat just in case my stomach gets really (hu|a)ngry. This tends to be the initial mornings---I wake up super hungry because it's still 13-14h for me, and my body wants its lunch and wants it now. Luckily it tends to mellow as days pass by.
MOVE!If you're a couch potato during the day, your body has absolutely no motivation to sleep. Your brain might be tired but that's it--your muscles still have energy to burn and metabolism needs to happen for you to function. Try to walk at least an hour, or run, whatever. Since you'll be waking up at insanely early hours--say 5-6 AM-- it might be good to use that extra time to do some exercise. Then get a shower and have breakfast earlier than everyone else. I've also found that running before flying feels good because the muscles are tired and sitting sort of serves as healing time, weird as it might sound. Also when your body is "toned", it seem to resist extended sitting periods better.
I try not to, but if I'm really, really, really sleepy, I might do a power nap. This shouldn't last more than 15 minutes of actual sleep, and it does not include the time that takes you to fall asleep. For me that's about 7 minutes, so what I do is find some quiet place, and set an alarm for 15 + 7 = 23 minutes. When the alarm goes off, I wake up! No snoozing allowed!
If I do it this way I wake up quite refreshed, although the effects don't last as much as a full night of sleep would do.
For the curious: I found my average time-to-sleep by tracking my sleep with a fitbit, but it should work with any other activity tracker.
Caffeine during the day
I find a coffee in the morning works well to "clear the haze", and then maybe I will have another one and a coke, all spaced out by two-three hours intervals (this is a good chance to explore and find nice coffee places in the vicinity).
I don't do "energy drinks" because my heart just goes racing through the roof, and I'd rather keep it for longer.
Do, read or listen to something boring before sleeping
I have two books in my reader that never fail to induce sleep on me. One is Swann's way by Marcel Proust, and the other one is Capital by Karl Marx. Note I'm not judging their qualities---I'm just saying they cause a certain drowsiness on me. Other people have reported listening to the shipping forecast in a loop (listen to a forecast clip), but that didn't work for me.
I'd advise against doing anything minimally mentally stimulating before bed time. Specially avoid programming because your brain is going to be in SOLVING mode and that means you won't get any sleep, or very bad sleep, if at all.
Another option is to take a warm bath or a weak shower---I found that 'power shower'-style streams wake me up, so you might want to adjust the shower head or the water flow, and see if you can turn it into a "gentler" mode.
If everything else fails and you are actually tired, but still don't manage to sleep in the new timezone, you could also try these.
Melatonin is something you can't get in the UK unless you get a prescription, so I started trying valerian-based pills (you can get those in Boots). I was somewhat apprehensive of the idea of taking "sleep remedies" as I'm generally apprehensive of all pills, so I started easy.
The recommended dose was two pills, but I took only one. It produced a little bit of drowsiness on me--generally enough to "quiet the brain" and start sleeping. Two pills produce a stronger effect, but it wears off after about 4-5 hours. Sleep quality ranges from mediocre to acceptable and I usually wake up after that, but it's better than only 2 hours of light sleep.
I also tried melatonin recently, when I was in the States. The effect kicks in earlier and sleep quality felt way better. I slept for longer and woke up more rested next day. Also I felt like I had "shifted" a lot more to the new timezone, so much that I hardly had any coffee next day. I was a bit disappointed because I'd heard that melatonin induced super vivid dreams, but I didn't even remember what I dreamed. Boo!
And on the way back...
Again, you should try to adapt to the new timezone as soon as you board the plane. This will be fairly easy if you just spent a short time away :-)