Drink a lot of water. And when you're full of it and feel like you've had enough, drink some more. Water is the key to feeling good on the mountain and fighting altitude sickness. While you definitely don't want to overdo it (our guide told us a horror story of a man who drank 13 liters of water in one day — 13! — and had to be airlifted to the hospital), you do want to make sure you're drinking at least four liters a day. And when you're reaching the really high altitudes, bump it up to five or six. Yes, you'll pee a lot, and treating your water with iodine tablets is a pain, but your body will thank you.
Image Source: Caitlin Gallagher