One thing you can do is improve your muscle balance by training your legs with unilateral movements--exercises that work your legs individually, such as split squats, lateral lunges, single-leg squats, and single-leg Romanian deadlifts. This strengthens each leg individually, but it also improves the overall strength of your legs together to give you better stability and control on the board.
Thats more of a big-picture strategy for improving balance with your training, but dont forget to pay attention also to the finer points of your movement. When youre riding or training, think about
--Craig Friedman, Performance Specialist, Athletes Performance