The best way to prepare would be to train and sleep at altitude, but the next best thing is to increase your endurance and "cardio strength."
Building "cardio strength" means raising your peak VO2an indicator of how efficiently your body utilizes oxygen. The higher your VO2, the better shape you'll be in to handle the altitude.
Here's how to train:
1. To improve endurance, train at approximately 75 to 80 percent of your maximum heart rate (about 6-7 on a scale of 1-10 effort for those who don't use a heart rate monitor) twice a week for at least an hour.
2. To improve cardio strength, try intervals twice a week for the month of August. For instance, you can do 1- and 2-minute repeats for 30-45 minutes. You would warm-up, then do 1 minute of "work" at 90-95% intensity (an 8-9 level effort on a 1-10 scale) and then 1 minute walk. Do this five times, recover for 3-5 minutes, and then repeat. Continue for a total of 30-45 minutes.
3. Finally, take long walks another two days a week. Go for an hour or two just to get your body used to walking for long periods.
-- Paul Robbins, Metabolic Specialist, Athletes' Performance and Core Performance