Kona, Redline, or Cannondale. Choose the bike that fits within your budget and has the specifics that you prefer (i.e. geometry, SRAM vs Shimano, etc). Ride the bike on the less technical local mtb trails. All the time. Practice dismounts and remounts until you don't stress about them. See how low you can run the PSI before pinch-flatting. Find two trees about twenty yards apart from each other, and see how fast you can do figure eights around them. Find a steep hill that's about thirty yards long. Run up it while carrying your bike, remount at the top, ride down, then dismount. Repeat until you can't. Practice riding through the sandpits at the local grade school. Purchase Simon Burney's book and read it. Search youtube for superprestige.

Oh, and ride lots.