You cant add custom models to wow because the wow disable the custom models.
Did you add this as a geoset for the character model or a seperate .m2 that you wear as a helm?If you added it as a geoset the problem is most likely it is badly rigged.If you added it as a seperate model as a helmet, then the problem is most likely that the geometry is not in the center of the object.http://i.imgur.com/BUbcrw9.jpgLook at this image if you don't know what I mean. In this picture my geometry is not in the center of the model. (The object center point is only seen on selected submeshes).Don't listen to ladiszlai he is trying to trick you into some bullshit.
[media:djx3g8hw]https://www.youtube.com/watch?v=MOcXlqo7w6Q[/media:djx3g8hw]if its Helm or Shoulder that doesnt mean method is samePs : lol i have to rework these tut my english suck and that how am i controling blender ... kill me ..