Q: What is the best exercise to develop balance on your mountain bike?
A: The best exercise for balance is the single leg deadlift. If forces you to balance in a very mountain bike specific position and movement.
For a bit more “exotic” balance drill I like to get on a swiss ball on my knees and balance there. It is very much like trying to keep your bike under you and you can have someone tap the ball and try to knock you off. It makes a fun little game, just don’t go overboard and get hurt!