The biggest mistake people make when trying to blanket a spooky horse is sneaking the blanket up on the horse. If you reach the blanket up towards the horse and he has a heart attack, repeat the same motion another hundred times. When he relaxes, retreat and rub him. Then do it again. A lot of people mean well, but they end up doing it all wrong. They sneak the blanket up to the horse, and he gets scared and tries to move. So the person tries to stop him from moving by shortening up on the lead shank. The more they try to stop the horse from moving, the more trapped and claustrophobic he feels, which makes him want to resist the blanket even more. That’s actually the complete opposite of what you want to have happen.
If the horse wants to move, keep moving the scary object, in this case the blanket, and keep his head tipped towards you. When his feet stop moving and he relaxes, that’s when you retreat and take the blanket away. A lot of people take the object the horse is scared of away when the horse moves. Only take the blanket away when he stands still and relaxes.