When I studied abroad in London, the hardest part wasn't being far from my family, or dealing with culture shock, or keeping up with my school work - it was surviving the flight from LAX to Heathrow. Looking back, I could have made the 13-some hours a lot less painful if I had only taken a few prep steps.
Get your entertainment ready:
Charge up all your devices. Download movies, stock up on books on your e-readers, and paper to doodle. Invest in a quality pair of headphones and make a great playlist ahead of time (one for sleepy time and one for improving your mood)
Wear comfy clothes on the plane. While I can't stand sweatpants, I fully support leggings and cardigans. It's all about the layers. Sometimes I'm freezing on a plane and sometimes I wake up from a nap sweating! Think about bringing a scarf to use a blanket.
Quench your thirst:
Hydration is everything. Buy a bottle of water and get water every chance you can from the stewardesses. Bring light foods that won't make you thirstier. As for snacks, I’ll bring along vegetable sticks, fresh fruit (NOT bananas – the smell is too strong), and almonds.