There is a drill we do in martial arts that will help.
It’s called the Four Corner Balance Drill (4CBD). Here is a video http://youtu.be/RpMDLWzLMRg
There is also the towel stretch which will increase flexibility and stability of the foot. Stand with a towel placed underneath your feet. Use your toes to scrunch up the towel and hold the position for 10 to 20 seconds and relax. Straighten out the towel with your toes and repeat the exercise for five sets total.