Posture has everything to do with neck and jaw alignment.  Perhaps the greatest way to learn efficient head and neck posture is through the Alexander Technique.  Margi, who is a very seasoned Alexander practitioner, draws on her knowledge and experience to guide us into finding proper head and neck posture.  She teaches us how to  "un-do" habits of tensing and clenching, while replacing them with sensations of expansion and spaciousness.  This lesson comes in 3 parts.  Visit www.poisealexander.com for more info