All you need to do is to direct your attention to the external effects of your movements on the environment rather than to the movements of your own body. Data supporting the effectiveness of this simple technique were published in the February 2009 issue of Physical Therapy, the scientific journal of the American Physical Therapy Association (APTA). Lead researcher Gabriele Wulf, PhD, and her team observed 14 persons with PD as they used differing focusing strategies when trying to balance on an unstable surface. When participants focused on the effects of their movements on the unstable surface they had fewer postural instabilities than when they focused on their own body (e.g. what their feet were doing.).
Gabriele Wulf, Merrill Landers, Rebecca Lewthwaite and Thomas Töllner, (2009). External Focus Instructions Reduce Postural Instability in Individuals With Parkinson Disease. M Physical Therapy, 89, (2): 162-168.