The importance of lowering the back of the tongue and lifting up the soft palate to create more space in your oral cavity and phyarnx, when one is singing high notes, cannot be stressed enough. This must be done in a relaxed, effortless manner. The amount of this created space will depend on how high a pitch you are at in your voice and at what volume you are singing at.
When inhaling air to begin a vocal phrase, take the air in through both the nose and along the roof of the mouth. This will help to achieve a better oral cavity position and a better chance for proper vocal resonance.
The National Association of Teachers of Singing
http://www.nats.org
The Classical Singer
http://www.classicalsinger.com
The Voice Foundation
http://www.voicefoundation.org/
The American Speech-Language-Hearing Association
http://www.asha.org
The New York Singing Teachers Association, Inc.
http://www.nyst.org
