Here are a few videos from my YouTube page and a few blog posts that will help you with a few of the fundamental elements of Mountain Bike riding:
Essential mountain biking skills
Why your crashing!
Mtb pedals, which kind is right for me?
Essential mountain biking skills
Why your crashing!
Mtb pedals, which kind is right for me?
Maintaining Attack position
Mountain bike setup for beginners
Basic Single Track riding 101
Leveraged turn
Full Suspension shock setup (XC bikes)
Braking basics
Stems, long or short
Kick outs for tight turns and switchbacks
Tire Pressure
Make a 1x9 bike (One chainring in the front, 9 cog cassette in the rear)
Changing parts for a lighter Mtb
Trail Obstacles