For better balance and to prevent chipping when trotting or loping over trail poles; approach the obstacle and ride over the obstacle with one arm extended forward.  The arm should be shoulder level with the finger tips up at eye level.  As you approach the obstacle pretend to press your hand into a wall.  Keep your eyes and chin up as well.  This exercise will prevent the rider from falling forward and causing the horse to lose cadence and chip into the obstacle. 
TRAINING TIP FOR TRAIL
Maintain Balance While Crossing Poles