I live at about 100-200 feet above sea level, so it is possible for us flat landers to do BTC.

I took (some of) the advice from another thread here on dealing with altitude sickness - mostly in drinking a lot of water and avoiding caffeine and alcohol for a few days before the ride. I flew to Durango the day before the ride started, maybe not ideal for acclimatization, but we did do an easy 5 mile ride around town which I think helped.

Riding hills for several months in advance was the best preparation, though . Oh, and having a broken computer mount so I never had to see just how slow I was going. That was important too.