Patience is Golden Rule
With time and patience you can teach your horse to accept anything around his head, neck and body, thus preventing any spooking out on the trails or in the arena. There are several simple excercises that will help you develop trust and confidence with your horse.
Safety is the most important thing to always consider when introducing something new to your horse. Stand at his shoulder, use your right hand to place on his neck and your left to hold and control the rope. Place a short piece of rope around your horses poll, through his mouth like a bit and feed the end through a loop at the other end of the rope. (See photos for clarity). Take care not to allow the rope to drape to the floor or you may step on the end of the rope resulting in punishing your horse at the wrong moment and setting you back in your work.
First start with the rope excercise to lower your horses head, put your hand on your horses neck and gently ask him to lower his head, if he resists simply put pressure on the rope by pulling downward, the second he drops his head release the pressure and repeat until all you have to do is rest your hand on his neck just below his ears.
Gradually put more pressure on him by using a plastic bag or a piece of plastic wrap to rub on his neck and body, never release the pressure if he is tense and moving away from you.
Working on the ground will improve your work in the saddle tremendously. This is a highly effective excercise with any horse at any time in his training.