When it comes to international flying, you'll soon learn that East is least and West is best. Always will have a tougher time adjusting when going east.

As mentioned above, sleep in the bunk. If you can't sleep on the airplane, bid domestic.

The key to making the best of your layovers is discipline. If you need a powernap (and powernaps are great) then set an alarm for an hour later and do wake up when it rings.
If you oversleep then you'll feel like crap the rest of the day.

Hitting the gym for a light workout helps with the body clock. Even though it's tempting to have that Wiener Schnitzel in Germany, eating light meals helps with the fatigue.
You probably don't wanna hear this but alcohol makes it difficult to sleep and makes you dehydrated. So by all means have a beer with the crew at dinner but if you overdo it then you'll be up all night (local time) stressing that you can't sleep.

When you get home you might be a zombie for a day or two.