Lots of good training advice already posted. I rode last year's event. My twopenneth is:
You need to be prepared to sit on your bike for 10 hours, so do at least 1 ride for that amount of time.
The riding is not technical, so get your bike as light as possible, as there's about 14,000ft of climbing.
It's a lot harder than the SDW in terms of climbing, but there are fewer steep climbs and lots of fireroads.
Work out on your long practice ride what you're going to eat and when.
The conditions last year were wet & gritty so you'll need spare brake pads, even if you've just fitted new ones. I needed new rotors as well as pads afterwards…
Sort your accommodation out now as there's a limited supply of rooms in the vicinity.
Good luck!