I'd offer these tips:
* Try to plan in advance when during the flights you'll sleep and when you'll try to be awake. Optimally, you'll want to try to get it to coincide with the time of day in Hong Kong.

* If you haven't used sleeping pills before, get a prescription now and see how they work for you. Or try various over-the-counter remedies. You don't want to experiment with unfamiliar meds on a flight.

* It's worth paying extra for optimal seats. Optimal means different things for different people, but it's worth it if it enables you to have a more comfortable flight.

* Load up on book, movies, magazines or whatever you need to entertain yourself.

* It's been a long time since I've flown through DFW, but if there's a lounge with showers or a hotel with day rooms you should consider paying for access so you can shower and nap, if it's a convenient time for you to nap, or even get a workout in.

* I find that many airline meals are too high in carbs, sodium and fat. Consider packing some snacks, sliced fruit or even lean protein (poached, sliced chicken with a chutney is one of my favs) that you can eat while flying GRU to DFW. You'll want to eat any fresh food -- plant or meat materials -- before clearing customs and immigration at DFW, since that is a big no-no with customs. You can buy more food at the DFW airport to carry onto your HKG flight.