It is good for you that you want training for Mountain Bike. But I recommended some [i:3ccdf3sb]Technique[/i:3ccdf3sb] that will help you for your future.
Balance – Balance is crucial in mountain biking, not just left-right balance, but front to back balance.
Climbing – Most riders will do at least some of their hardest climbs out of the saddle. It is necessary to rock the bike gently with each pedal stroke in order to keep the bike in a straight line.
Descending – Stay back on the bike.
Cornering – Learn the technique of "counter steering". Brake before corners, not in them. Look where you want to go, not at what you don’t want to hit. Bikes have a way of going wherever you look.
Braking – Most of your braking force is in the front brake. Use both brakes simultaneously, and brake before corners, not in them.
Shifting – You should always pick a gear that allows you to "spin" your pedals at between 60 and 90 rpm. (note: racers may spin more). Try counting your revolutions for 10 seconds, then multiply by 6, or get a cyclometer with a cadence (RPM) function.
Thanks,
Brooklyn Bridge Tour