If you are experiencing problems bridling your horse, check to make sure that the horse doesn't have a problem with its muzzle being handled in general. They may be ticklish on the muzzle or there may be a history of  being twitched or other things that would make the horse fear having its muzzle handled. There also may be an issue with the ears being handled. If either or both issues are present, they must be taken care of and thoroughly resolved before attempting to bridle your horse.
Trouble Bridling