IN THE STORE Sloping top tubes and radical frame shapes have made standover heightthe distance from the top tube to your crotcha worthless sizing gauge. The only way to know for sure if a bike fits is to ride it. If a shop won't let you, go to the competition. As shocks have improved, they've become more complex: You'll have to master their dial-in settings for your weight and riding style.
IN THE FIELD Carry a full multitooland know how to use it. Depending on how far into the wilds you've ridden, damaging your bikeand you will damage your bikecan range from annoyance to Deliverance. Climb in the saddle whenever possible: Standing throws your weight forward, making it harder for your rear wheel to dig in. Clean your bike after every ride. Proper upkeep, especially of the drivetrain, is doubly important on mountain bikes.
IN THE FUTURE GT and Honda (yes, that Honda) have developed downhill bikes with internal gearboxes. Huskier and more reliable than derailleurs, these inventions let riders shift gears even when they're not pedalinga boon during technical descents. If refinements can get the weight down, the century-old derailleur may finally become a thing of the past.