Before you do anything buy a Clymer Service Manual.
Next, read the forums, read, read and read some more.
Learn to tune your carbs.
Tuning>> FAST Carb Sync Tool
Tuning>> Digital Tach from eBay
Learn about essential tools and how they work.
Compression tester obviously, but what about a leakdown tester?
Suspension mods are key to Duning and Desert riding.
Look into aftermarket fat bars and an anti-vibe steering stem. Huge in the handling department. I have a +2+1 taller and forward Fireball steering stem coupled with Pro Taper Contour 1-1/8" with ODI Rogue clamp on grips and OMG what a difference. I was immediately way faster due to a huge confidence boost in the control and handling department.
Fireball Racing for control arms and swingarm. BVC Racing for Stage 3 Elka front and rear shocks. Delete the airbox in favor of K&N filters and Outerwears mounted directly to the carbs. Like DuneCat mentioned, TORS Delete Stock Intakes Mod'd for VF4's and retain stock cross-over tube V Force 4 Reeds A nice set of pipes for Desert and Dunes is CPI. They're more of a drag pipe than say FMF or Toomey T5's. Trinity Stage 4 pipes are a very good pipe if you can find some. Look into DMC pipes. SLP is another good pipe that makes a shit ton of power, but signs off about 1k rpm sooner than say CPI. Billet Chariot or Mattoon timing plate set to +4*.
And don't forget about maintenance.