Two recommendations:
1. Make sure you have a place to ride, and people to ride with, even if they don't mountainboard (ie go with some mountain bikers or something). Dirt jumps, skatepark, whatever.
2. If you're riding anything where you don't have enough space to do big turns, I would buy brakes. You can do downhill riding without them, but you have to be good and its hard.
I didn't really have anyone to ride with, and no brakes, so I barely used mine last year. I think I'll pick up some brakes next week though, and get back at it.