The path of the point of tire contact with the ground will tend to form two superimposed mirror-image S curves whose ends meet (a figure eight!). At each end of the idle cycle, the point where the ends of the S curves meet is where you do an action-reaction twist and reverse the direction of wheel rotation. This pattern is short and narrow, about 6 inches long and 2 wide with a 24" wheel. With practice it will become even smaller.
I first saw this technique demonstrated on George Peck's "Rough Terrain Unicycling" videotape. It is an important technique for offroad riding as well as uni basketball and hockey because it allows you to move off almost instantly on a power stroke instead of waiting a beat for the pedals get into a good position to start moving.