Preparing for the high elevations involves as much physical conditioning as you can manage. If you’re fortunate enough to have mountains (over 8,000 feet) and a few nights off available, hiking the trails and sleeping at elevation will pay off great dividends as you start to push your body’s ability to adapt to ever decreasing oxygen volume. At over 8,000 feet (I definitely start to feel it at 9,000 feet) you’ll find that simple exertion will get your system a little worked up, with a higher heart and breathing rate. The idea of spending some time in the mountains, besides the fresh air, is to give your body a little advanced warning and so it will have an easier time getting in gear when you really do go trekking.