Before you come
Start drinking water early
The single biggest thing you can do.
The town's visitor guide suggests 2 to 3 liters of water a day in the days before your trip, and about twice what you'd normally drink once you're here. Electrolyte drinks help. The air is dry as well as thin, so you lose more water than you notice.
Day one
Take it easy
Ski the lower peaks first.
Don't go straight to Imperial on your first morning. The resort suggests spending day one on Peak 9 or Peak 7 and moving up to the high bowls once you've adjusted. Stop for snacks more often than you would at home.
In the evening
Go easy on alcohol
It hits harder up here.
Alcohol and caffeine both slow down how well you adjust. If you're drinking, have a glass of water with each one. The first night is when most people overdo it.
At night
Sleep
Thin air makes for restless nights.
Poor sleep is one of the common signs of altitude, and dry air makes it worse. Many hotels and rentals have humidifiers. Ask for one.
Know the signs
Altitude sickness
Headache, nausea, tiredness.
Mild altitude sickness usually means a headache, dizziness, nausea, poor appetite, bad sleep and feeling tired. Rest and water often sort it out. If symptoms are severe or get worse, see a doctor. The nearest hospital is in Frisco.