I travel often for both work and play.  I love it.  It can also be dreary and take a toll on the body but there are ways to cope.  Here’s what works for me:

• BYO: I almost never eat plane (or train) food.  It’s typically very processed, sits in the stomach and generally makes me feel awful.  Instead, I try to bring healthy-ish snacks with me to the airport (like nuts, chocolate, fruit).  At the airport, avoid the temptation of that burrito or sausage and opt for a salad or bowl of noodles instead – the Pret, Eat or Itsu locations at Heathrow provide decent options.
• Hydrate: On the plane, I try to drink lots of water and use lotion to keep the skin hydrated.  In terms of alcohol, I’ll usually have a glass of red with a meal and to help me sleep but rarely more than that.   
• Sweat it out: I’ve found working out to be one of the best ways to beat jetlag.  I can’t bear the monotony of gyms.  Instead, I try to find a yoga class in the city I’m visiting or, occasionally, see if I can line up a game of squash.  Barring that, walking or jogging is a great way to get exercise and see the city.
• Travel light & avoid cotton: Usually there’s no need to bring separate outfits for each day.  I can often get away with a pair of slacks and jeans or even just jeans for a trip.  I avoid cotton and opt instead for fast-drying synthetic clothing.
• Get stuck in: Sometimes there are unavoidable business trips where you're so busy in meetings and hotel rooms the whole time that it doesn’t matter where you are.  Otherwise, I try to build in some time to see even a bit of the place I'm in.  I once had just two hours of free time in Rome before having to leave for the airport and used it to walk around, grab a gelato and people-watch.  It was memorable and beat sitting around the airport.  I don’t worry about making it to museums or the standard tourist attractions – most of them are closed when I'd have free time anyway.  Instead, I try to walk or take public transportation to my meetings [N.B. this is much more easily done in Europe than North America or Asia].  It forces me to learn the city's geography and get a better feel for the place and people.
• Rest: I try to build in some downtime during my trips and, especially, when I get back, to give my body time to recover.  I don't always do this and have learned the consequences the hard way.